- check_circleConfirm the circuit breaker is on and has not tripped. For hybrid models, verify both poles of the 240 V breaker are engaged.
- check_circleConfirm the gas shutoff valve is fully open (handle parallel to the pipe) for gas units.
- check_circleConfirm the cold-water inlet valve is fully open.
- check_circleCheck the display for an error code — write it down exactly before taking any action.
- check_circleConfirm the unit is not in Vacation mode or a low-output operating mode.
- check_circleDo not repeatedly reset the unit if the breaker trips again or the same error code returns.
- check_circleIf the unit has never worked correctly since installation, contact the installer first.
Last updated: June 11, 2026. Troubleshooting steps depend on the exact Rheem model. Always follow the user manual for your specific unit. Local building, gas, electrical, and plumbing codes may vary.
Installation and startup issues — not a defective appliance — are the most common reason a brand-new Rheem water heater fails to produce hot water.
If your brand-new Rheem water heater is not working, take a breath before assuming the unit itself is defective. In the majority of cases, a newly installed water heater that fails to produce hot water has not been correctly commissioned, is missing power or gas supply, has a valve left closed, or has not yet completed the initial startup sequence.
Other common scenarios include a tank that was energized before it was completely filled with water, air in a new gas line preventing ignition, an incorrect thermostat setting, a configuration error on a smart unit, or a venting problem that is preventing the unit from firing safely. Genuine manufacturing defects exist, but they are far less common than installation or setup problems.
This guide walks through the safe checks you can perform as a homeowner, explains common causes for each type of Rheem unit — gas, electric, tankless, and hybrid heat pump — and tells you clearly when to contact the installer, Rheem warranty support, or a licensed technician.
Is It Normal for a New Rheem Water Heater to Take Time to Heat?
Yes — a storage tank water heater does not produce hot water instantly after installation. When a brand-new tank is filled for the first time, it contains cold water that must be heated from the incoming groundwater temperature up to the thermostat setpoint. This initial heat-up period takes time and varies based on the tank capacity, fuel type, thermostat setting, heating element or burner capacity, and the incoming cold-water temperature.
In Canadian provinces and northern U.S. states during winter, groundwater can arrive at 35°F to 45°F (approximately 2°C to 7°C). A full 50-gallon tank starting from that temperature will take considerably longer to reach its set point than the same tank in warmer climates. Do not assume the unit is defective simply because hot water is not available immediately after installation.
Tankless water heaters behave differently — they heat water on demand and do not maintain a stored supply. There is no initial warm-up period for the water, though the burner does have a brief ignition sequence before hot water flows. If a tankless unit fails to activate at all, that is not a waiting issue — it is likely a flow, power, gas, or configuration issue covered later in this guide.
Hybrid heat-pump water heaters may also behave unexpectedly in the first few hours depending on the operating mode selected. In Heat Pump mode, recovery is slower but more energy-efficient. In High Demand mode, both the heat pump and the electric resistance elements run simultaneously for faster recovery. If the unit was left in Heat Pump mode after installation and the household demand is high, it may appear to be underperforming when it is simply working as designed in that mode.
Brand-New Rheem Water Heater Not Working: Start With These Checks
Before contacting anyone, work through this safe homeowner checklist. Do not open electrical access panels, adjust gas valve internals, bypass safety switches, or dismantle any part of the appliance.
- check_circle
Confirm that the installation has been completed and the unit was commissioned by the installer.
- power
Check the circuit breaker at the electrical panel — push firmly to OFF, then back to ON if tripped.
- toggle_on
Check for a nearby disconnect switch (box near the unit) and confirm it is in the ON position.
- gas_meter
Verify that the gas shutoff valve feeding the water heater is fully open (handle parallel to the pipe).
- water_drop
Confirm the cold-water inlet valve is fully open and that faucets in the home have normal water pressure.
- thermostat
Check the thermostat setting or temperature display on the unit — it may be set very low.
- do_not_disturb_on
Confirm the unit is not in Vacation mode or a low-energy mode that limits hot water output.
- error
Check the display panel for any error code or status message and write it down exactly.
- water
Look for visible water leaks at connections, fittings, or the temperature and pressure relief valve.
- visibility
Confirm that no service valve was left closed by the installer — including isolation valves at the unit.
- menu_book
Locate the user manual for your exact model and read the initial startup section.
- photo_camera
Photograph any error codes, unusual conditions, or installation details before contacting anyone.
Important: Do not open the electrical access panels on the side of the unit, attempt to adjust internal gas components, bypass safety controls, or press the high-temperature reset button (where applicable) without understanding why it activated. These actions can create safety hazards and may affect your warranty coverage.
Rheem Water Heater Troubleshooting Table
| Symptom | Possible Cause | Safe Check | Who to Contact |
|---|---|---|---|
| No hot water at all | Breaker off, gas valve closed, unit not commissioned, tank not filled (electric) | Confirm breaker is on, gas valve is open (handle parallel to pipe), cold-water inlet is open | Installer if not commissioned; electrician if breaker issue |
| Water is only lukewarm | Thermostat too low, mixing valve installed, reversed connections, undersized unit | Check temperature/thermostat setting on display or dial; confirm no mixing valve at outlet | Installer for plumbing or configuration issue |
| Unit has no power / blank display | Breaker tripped, disconnect switch off, only one pole of 240 V breaker engaged | Check breaker panel and nearby disconnect; for hybrid units check both poles of breaker | Licensed electrician if breaker trips again |
| Pilot or burner does not start | Gas valve closed, air in new gas line, startup procedure incomplete, venting incomplete | Confirm gas supply is active and valve is open; follow startup sequence in user manual | Installer; gas utility if supply issue suspected |
| Tankless unit does not activate | Flow below activation threshold, service valve closed, inlet filter blocked, crossover | Confirm all service valves are fully open; check for error code on display | Installer to verify commissioning and valve positions |
| Water temperature fluctuates | Flow rate variations, undersized unit, cold-water crossover, improper recirculation | Check whether multiple fixtures are running simultaneously; review mode settings | Installer if plumbing crossover or sizing is suspected |
| Error code on display | Varies by model — ignition, flow, venting, sensor, temperature, or communication fault | Note the exact code; look up your specific model manual at rheem.com | Installer first; Rheem support if code indicates a component fault |
| Unusual noise | Normal expansion noise, air in pipes, sediment (rare in new unit), heat pump fan | Confirm cold-water supply is fully open; allow pipes to purge air after first fill | Installer if noise is persistent or sounds like water hammer or hissing |
| Water leaking from unit | Loose fittings, T&P valve discharging, condensate drain, incomplete connections | Identify where water is coming from; do not ignore leaks near electrical components | Installer immediately; electrician if water is near electrical components |
| Breaker repeatedly trips | Circuit undersized, incorrect wiring, component fault | Do not reset a breaker that trips immediately — note and document | Licensed electrician; installer if wiring is incorrect |
| Hot water runs out quickly | Unit undersized for demand, thermostat low, hybrid in low-output mode, cold crossover | Check temperature setting and operating mode (hybrid); confirm no crossover plumbing | Installer to verify unit sizing and configuration |
| Hybrid unit stays in electric-only mode | Ambient air too cold or too hot, insufficient airspace, filter clogged, mode setting | Check operating mode on display; confirm installation space temperature and airflow | Installer to verify space requirements and mode configuration |
Possible causes listed above are general. Your exact model's user manual takes priority for diagnosis. Error codes, reset procedures, and component locations vary between product families.
Key rule
A brand-new unit that has never worked correctly since installation is almost always an installation or commissioning issue — contact the installer before assuming the appliance is defective.
New Rheem Electric Water Heater Not Heating
A Rheem electric water heater that produces no hot water after installation typically comes down to one of several common causes. The most critical — and most frequently overlooked — is that the tank was not completely filled with water before power was applied.
Electric heating elements are submerged in water inside the tank. If the tank is empty or only partially filled when the breaker is switched on, the elements heat in air rather than water — a condition called dry firing. Dry firing can permanently destroy the heating elements and may void the warranty. Before energizing any new electric water heater, the tank must be completely filled: open a hot-water faucet inside the home, open the cold-water supply valve to the heater, and wait until a steady stream of water flows from the open faucet before applying power.[1]
Common causes for a new Rheem electric water heater not heating
- arrow_rightCircuit breaker is off or has tripped — check the electrical panel
- arrow_rightNearby disconnect switch is in the OFF position
- arrow_rightOnly one pole of the 240 V double-pole breaker engaged (unit receives 120 V instead of 240 V — common on hybrid models)
- arrow_rightTank was not completely filled before power was applied (dry firing)
- arrow_rightThermostat is set very low — check temperature setting on the unit
- arrow_rightWiring connections at the unit are incorrect or loose (installer issue)
- arrow_rightHigh-temperature limit (thermal cutoff) has activated — may require reset per user manual
- arrow_rightUtility power issue affecting the home
Safety: Do not open the electrical access panels on the side of the tank, touch wiring terminals, test live conductors, or attempt to replace heating elements yourself. If you suspect a wiring error, an incorrectly sized circuit, or a breaker that trips immediately, contact the installer and a licensed electrician. Do not reset a breaker that trips immediately after being switched on.
New Rheem Gas Water Heater Not Working
A new Rheem gas water heater that will not ignite is one of the most common new-installation problems. The majority of these cases are not caused by a defective unit. In most situations, the gas supply is not active, the shutoff valve is not fully open, or air trapped in the newly connected gas line is preventing ignition.
When a gas line is newly installed or reconnected, air occupies the pipe from the point of disconnection to the appliance. Before the burner can ignite, this air must be displaced by gas. In a new installation, this purging process can take multiple ignition attempts — sometimes five to fifteen attempts with brief pauses between — before enough air is cleared and the burner lights reliably. This is normal behaviour for a newly installed gas appliance and is not a sign of a defective unit.[2]
Common causes for a new Rheem gas water heater not working
- arrow_rightGas shutoff valve at the water heater is closed or only partially open
- arrow_rightGas service to the home is not active — confirm with other appliances
- arrow_rightAir in the new gas line — multiple ignition attempts may be required to purge
- arrow_rightPilot or ignition startup sequence was not completed correctly — follow the exact user manual
- arrow_rightVenting is incomplete, incorrect, or not fully connected before startup
- arrow_rightCombustion air supply is restricted by an incomplete or blocked intake
- arrow_rightCondensate drain not installed correctly on applicable condensing models
- arrow_rightControl valve or gas pressure not configured for the local gas type (natural gas vs. propane)
- arrow_rightUnit displays an ignition or airflow error code
Gas Safety Warning
If you smell gas near the water heater or anywhere in your home, stop what you are doing immediately. Do not operate any electrical switches, light any open flames, or use your phone inside the building. Leave the building, leaving the door open behind you, and move well away from the structure. Call your gas utility or emergency services from a safe location. Do not re-enter until the gas company has confirmed the building is safe.
New Rheem Tankless Water Heater Not Working
Tankless water heaters operate fundamentally differently from storage tank units. A tankless unit does not heat water continuously — it fires the burner (or activates the heating element for electric models) only when a hot-water tap is opened and flow reaches a minimum activation threshold. If the flow rate falls below this threshold, the unit will not activate at all, and no amount of waiting will produce hot water.
This minimum activation flow rate varies by model — consult your specific unit's user manual for the exact specification. Partially closed service valves, a clogged inlet filter screen that was not cleared before commissioning, very low-flow fixtures, or a plumbing crossover where cold water is backing into the hot-water line can all prevent the unit from reaching its activation threshold.
Common causes for a new Rheem tankless water heater not working
In cold Canadian climates and northern U.S. states, incoming groundwater temperatures in winter reduce the maximum hot-water output a tankless unit can deliver at a given flow rate. If the unit is producing warm but not fully hot water, the issue may be that the temperature rise — the difference between the incoming cold water temperature and the desired output temperature — exceeds the unit's capacity at the current flow rate. Reducing the flow rate slightly or confirming that the unit is correctly sized for winter conditions may resolve this.
New Rheem Hybrid Heat-Pump Water Heater Not Working
The Rheem ProTerra hybrid heat-pump water heater is the most complex product in Rheem's residential lineup, and new-installation problems are often related to operating mode, electrical supply, or installation space rather than a unit defect.
Operating Modes on the ProTerra
The ProTerra offers five operating modes, each with different performance and efficiency characteristics.[3] Understanding these modes helps explain why the unit may appear to be underperforming immediately after installation:
Energy Saver (default)
Uses heat pump and electric backup intelligently. Default mode at installation. Provides good efficiency but recovery is slower than High Demand mode.
Heat Pump Only
Uses only the heat pump compressor. Most efficient but slowest recovery. Not recommended for high-demand periods.
Electric Only
Resistance elements only — heat pump off. Recommended during maintenance, filter cleaning, or when ambient temperature is too low for the heat pump.
High Demand
Runs both heat pump and electric elements simultaneously for fastest recovery. Higher energy use but best hot-water availability.
Vacation / Away
Reduces operation to a minimum — the unit may appear to produce no hot water if left in this mode after installation.
Other Common Hybrid Installation Issues
- arrow_rightBoth poles of the 240 V double-pole circuit breaker must be fully engaged — one active half results in the unit receiving only 120 V, which is insufficient
- arrow_rightThe unit requires adequate surrounding air space — check your model's specification for the minimum cubic footage; insufficient airspace reduces heat pump efficiency
- arrow_rightAmbient air temperature must be within the unit's operating range — confirm the minimum temperature specification for your exact model
- arrow_rightThe condensate drain must be correctly installed and draining freely before startup
- arrow_rightAir intake and discharge must not be obstructed — the heat pump moves air to function; check that the installation space is clear
- arrow_rightVacation or energy-saving mode may have been accidentally activated during installation
- arrow_rightThe unit may display a startup message or initialisation indicator for the first hour of operation
If the hybrid unit displays an error code or fails to produce any hot water after confirming the electrical supply and operating mode, contact the installer. The ProTerra's heat pump system has refrigerant components that require factory-authorized service — do not attempt to open the refrigerant circuit.
Why a New Water Heater Produces Only Lukewarm Water
Lukewarm output is one of the most common complaints after a new water heater installation, and the cause is often not the water heater itself. Before assuming the unit is underperforming, check these possibilities:
Thermostat or temperature setting is too low
The default factory setting on many Rheem models may not match the previous homeowner's preference. Check the temperature dial or digital setting on the unit and confirm it is set to your desired output temperature. The U.S. Department of Energy recommends 120°F (49°C) as a safe and energy-efficient default.
Anti-scald mixing valve or tempering valve at the outlet
Many plumbers install a mixing or tempering valve at the water heater outlet to prevent scalding. This valve blends cold water with the hot supply and caps the temperature delivered to the home. If this valve is set very low or was incorrectly adjusted during installation, it can produce lukewarm water at every tap regardless of the heater's actual output temperature.
Reversed hot and cold plumbing connections
If the installer connected the hot outlet pipe to the cold inlet and vice versa, cold water will flow into the tank while hot water exits through the cold supply — producing lukewarm water at all taps. This can be confirmed by a qualified plumber.
Cold-water crossover through a shared cartridge
A worn or faulty single-handle shower valve or faucet cartridge can allow cold water to pass into the hot-water line. This dilutes the hot water supply throughout the home and may cause the water heater to run continuously. The problem will appear to follow the water heater, but the actual cause is at the fixture.
Tankless temperature rise insufficient for cold climates
In cold Canadian provinces and northern U.S. states, a tankless unit that is correctly sized for summer conditions may struggle to achieve the full temperature rise in winter when groundwater arrives much colder. This is a sizing and specification issue, not a unit fault.
Long plumbing runs losing heat before the tap
In a large home, hot water travelling through long, uninsulated pipes loses heat before reaching distant fixtures. The water heater is performing correctly — the heat is being lost in transit. Pipe insulation or a recirculation system can address this.
Installation Problems That Can Affect a Brand-New Rheem Unit
The following items are common installation-related causes of new water heater problems. They are presented neutrally — most experienced, licensed plumbers and HVAC technicians complete these steps correctly. When they are missed, they are the installer's responsibility to correct, not the homeowner's.
If you suspect any of the above contributed to your problem, contact the installer. A licensed contractor is responsible for verifying all of these items as part of a complete installation. Keep your installation invoice, the installer's business information, and any photos or videos documenting the problem.
Troubleshooting Priorities by Rheem Water Heater Type
| Rheem Type | First Items to Check | Common Installation Concern | Professional Needed When |
|---|---|---|---|
| Electric tank | Breaker on; disconnect on; tank fully filled with water before power was applied; thermostat setting | Tank energized before being completely filled with water (can destroy heating elements) | Breaker trips; wiring error suspected; unit shows no response after correct startup |
| Gas tank | Gas shutoff valve open; gas service active; startup sequence followed; multiple purging attempts for air in new line | Air in new gas line; incorrect vent size or routing; venting not fully connected before startup | Ignition fails after multiple attempts; gas smell at any time; error code on display |
| Tankless (gas or electric) | Service valves fully open; inlet filter screen clean; flow rate above activation minimum; error code on display | Undersized for peak demand; cold-water crossover; reversed connections; venting incomplete (gas) | Error code persists; burner will not fire after valves confirmed open; flow rate confirmed adequate but unit still inactive |
| Hybrid heat pump | Both poles of 240 V breaker engaged; operating mode selected; installation space temperature and airflow adequate | Insufficient air volume around unit; condensate drain incomplete; incorrect mode selected at commissioning | Unit displays fault code; heat pump runs but produces no heat; breaker trips; condensate leaking |
Should You Reset a New Rheem Water Heater?
A reset can sometimes clear a temporary fault — a momentary power fluctuation during startup, for example — and allow the unit to operate normally. However, reset procedures vary significantly between Rheem models. There is no single universal reset sequence that applies to all Rheem gas, electric, tankless, and hybrid water heaters. Follow the exact procedure described in the user manual for your specific model.
What you should not do: do not repeatedly reset the unit if the same error code returns immediately after each reset, and do not keep switching the circuit breaker on and off if it trips immediately. A breaker that trips repeatedly is protecting the circuit from a real electrical problem — resetting it repeatedly without diagnosing the cause risks damaging the appliance or creating a safety hazard.
Similarly, recurring error codes are not cleared by resetting — they return because the underlying condition that triggered them has not been corrected. Clearing a code and attempting to operate the unit without diagnosing the cause does not solve the problem; it only temporarily hides it. If the same code appears after a reset, treat it as a persistent fault that requires professional diagnosis.
Understanding Rheem Error Codes
Rheem water heaters use diagnostic codes to communicate fault conditions. The format, meaning, and reset procedure for these codes vary substantially between product families. A code that means ignition failure on one series may mean something entirely different on another. Error codes on gas tankless models differ from those on electric models, which differ again from hybrid models.
When you see an error code, write down the exact code displayed — including any letter prefix or suffix — before taking any action. Then locate your model number (on the label on the side or back of the unit) and serial number, and look up the exact code in your unit's official user manual or at Rheem's support website. Do not use a code reference from a different model — even small differences in the product series can mean different causes and procedures.
Some codes indicate temporary conditions — a brief power fluctuation, for example — and may clear on their own or after a single reset. Other codes relate to persistent faults such as ignition failure, blocked airflow, temperature sensor malfunctions, water flow problems, or venting issues. These codes will return until the underlying cause is corrected.
For Rheem tankless error codes, see our Rheem Tankless Error Codes guide for code-by-code explanations. For error code 11 (no ignition) specifically, see our Rheem Error Code 11 troubleshooting guide. Always cross-reference with your exact model's official manual.
When to Call the Installer
In the majority of cases where a brand-new Rheem water heater is not working correctly, the original installer should be your first call — not Rheem warranty support. A licensed contractor who has just completed an installation is responsible for ensuring the unit was correctly commissioned and is producing hot water before leaving.
Contact the installer when:
- arrow_rightThe unit has never produced hot water since installation
- arrow_rightThe installation was completed within the past few weeks
- arrow_rightThe system has no power or the breaker trips immediately
- arrow_rightGas ignition does not occur after following the startup procedure
- arrow_rightValves or plumbing connections appear to be incorrectly configured
- arrow_rightError codes appeared immediately after installation
- arrow_rightVenting, condensate drainage, or airflow problems are suspected
- arrow_rightWater is leaking from connections or fittings
- arrow_rightThe unit was never tested after installation
Information to have ready for the installer
Seeing an error code? Get a guided diagnosis.
HeatSync covers Rheem gas, electric, tankless, and hybrid models. Enter your unit type and symptom for a structured yes/no diagnostic flow built from OEM procedures. Free, works offline.
When to Contact Rheem Warranty Support
Contact Rheem warranty support after you have confirmed or ruled out an installation issue. Rheem's warranty does not cover problems caused by incorrect installation, so submitting a warranty claim for an issue that is actually an installation error will delay resolution and may not be honored.
Warranty coverage varies by model series — terms for a standard electric tank differ from those for a condensing gas tankless unit or the ProTerra hybrid. Coverage typically includes a component parts warranty and a limited tank or heat-exchanger warranty; labour coverage under the standard warranty is generally limited.[4] Verify the specific warranty terms for your exact model number at rheem.com/warranties.
To protect your warranty rights: register the unit at rheem.com within the required period (typically 60 days of installation), retain your installation invoice as proof of professional installation, and keep your model and serial number accessible. Rheem may require diagnosis by an authorized service provider before approving a warranty claim.
Unauthorized modifications to the appliance or installation practices that do not comply with the manufacturer's installation instructions or applicable codes may affect coverage.
Should You Return a Brand-New Rheem Water Heater?
Returning a water heater should not be the automatic first step when a new unit does not work. Removing a just-installed water heater involves labour costs, potential permit implications, reinstallation of the old unit or installation of a replacement, and the risk of damaging components during removal.
Most new-unit problems are caused by installation or setup — not the appliance. Correcting an installation issue is almost always faster and less expensive than returning the unit. If a confirmed manufacturing defect exists after all installation issues have been ruled out, Rheem's warranty process typically covers parts replacement without requiring the entire unit to be returned to a retailer.
Retailer return policies vary — some have a limited return window after purchase, and returning a large water heater that has been installed typically falls outside standard consumer returns. Consult with the installer and Rheem before making any decision to remove and return the appliance. Document the problem thoroughly with photos, error codes, and a written description of symptoms before taking any action.
Safety: Stop and Call a Professional If Any of These Apply
Do not continue troubleshooting — contact a qualified professional immediately when:
- emergencyYou smell gas anywhere near the water heater or in your home — evacuate and call your gas utility from outside
- notifications_activeA carbon monoxide alarm activates — leave the building immediately and call emergency services
- boltThe circuit breaker trips repeatedly — do not reset again; call a licensed electrician
- cableWiring appears damaged, burned, or incorrectly connected
- waterWater is leaking near electrical components
- airVent piping is disconnected, damaged, or not connected to the unit
- local_fire_departmentThe burner repeatedly fails to hold a flame and the unit keeps locking out
- device_thermostatThe unit appears to be overheating or displays a high-temperature fault
- smoke_detectorThe appliance produces smoke, a burning smell, or visible combustion products
- water_pumpThe temperature and pressure relief (T&P) valve is discharging continuously — this is a serious safety indicator
Step-by-Step Decision Guide
Work through these questions in order. Answer each one before moving to the next.
Is there an active gas smell or water leak near electrical components?
Yes: Stop immediately — for gas: evacuate and call your gas utility. For electrical leaks: contact a licensed electrician.
No: Continue to Step 2.
Does the unit have power (display lit, fan running) or confirmed gas supply?
Yes: Continue to Step 3.
No: Check the breaker, disconnect switch, and gas valve before continuing. If the breaker trips again, stop and call an electrician.
Is the cold-water inlet valve fully open?
Yes: Continue to Step 4.
No: Open the cold-water supply valve and allow the tank to fill completely before restoring power or attempting startup.
Is there an error code on the display?
Yes: Write down the exact code and look it up in your model's user manual. Do not clear it until the cause is identified.
No: Continue to Step 5.
Was the unit properly commissioned and tested by the installer?
Yes: Continue to Step 6.
No: Contact the installer — incomplete commissioning is a common cause of new-unit problems.
Has the unit ever produced hot water since installation?
Yes: Continue to Step 7.
No: Contact the installer. A unit that has never worked suggests an installation issue.
Is the problem affecting all faucets, or just one?
All faucets: The water heater or its supply is likely the issue — continue troubleshooting.
One faucet: The problem may be at a specific fixture, mixing valve, or shutoff — check that faucet independently.
Is the original installer available and responsive?
Yes: Contact them first — they are responsible for correct commissioning of a recently installed unit.
No: Contact Rheem's technical support with your model number, serial number, and a description of the issue.
Do symptoms suggest a manufacturing defect rather than an installation issue?
Yes: Contact Rheem warranty support. Have your model number, serial number, installation date, and documentation ready.
No: Work with the installer to resolve the configuration or installation issue before considering a warranty claim.
Final Verdict: What to Do When Your Brand-New Rheem Water Heater Is Not Working
A brand-new Rheem water heater that is not working does not automatically mean the appliance is defective. In the vast majority of cases, the problem lies in power supply, gas supply, water valves, the startup procedure, configuration settings, venting, or installation.
Start with the safe homeowner checks: confirm the breaker is on, the gas valve is open, the cold-water inlet is open, and the unit has not been left in Vacation mode or an incorrect operating mode. Check the display for an error code and look it up in your model's official manual before taking any action.
If your brand-new Rheem water heater is not working correctly and has never produced hot water since the day of installation, the installer should be your first call — not the manufacturer warranty line. A qualified contractor is responsible for correctly commissioning the unit, and most new-installation problems can be resolved with a return visit to verify valves, wiring, venting, and configuration.
Document everything: the model number, serial number, installation date, a description of the symptoms, photos of the unit and installation, and any error codes displayed. This documentation protects you whether the resolution comes through the installer, Rheem's warranty support, or an independent licensed technician.
Frequently Asked Questions
Why is my brand-new Rheem water heater not heating?expand_more
A brand-new Rheem water heater may not heat due to incomplete installation, a tripped breaker or closed gas valve, a tank that was energized before being fully filled with water (electric models), air trapped in a new gas line, an incorrect startup procedure, or a configuration problem. Start with the basics: confirm power or gas supply, the cold-water inlet valve is open, and the startup instructions for your exact model have been followed.
How long should a new Rheem water heater take to heat?expand_more
A newly filled storage tank typically takes one to three hours to reach the set temperature, depending on tank size, fuel type, thermostat setting, and incoming water temperature. Gas models generally recover faster than electric models of the same capacity. Canadian homes with cold winter groundwater may experience longer initial heat-up times. Tankless units heat on demand and need no warm-up period. Hybrid heat-pump models take longer in Heat Pump mode than in Electric mode.
Why does my new Rheem water heater only produce lukewarm water?expand_more
Lukewarm output from a new Rheem unit is often caused by a thermostat set too low, an anti-scald mixing valve at the outlet blending in cold water, reversed hot and cold plumbing connections, or a tankless unit that is undersized for the temperature rise needed in a cold climate. Confirm the temperature setting on the unit, check for any mixing valves installed by the plumber, and ensure the hot and cold supply lines are connected correctly.
Should I reset my new Rheem water heater?expand_more
A single reset may clear a temporary fault, but reset procedures vary by model — always follow your unit's user manual exactly. Do not repeatedly reset the unit or keep switching the breaker on and off. A breaker that trips again or an error code that immediately returns after a reset indicates an unresolved problem. Repeated resetting without correcting the underlying cause can mask safety issues and delay proper diagnosis.
Why does my new Rheem water heater have no power?expand_more
Check the circuit breaker at the electrical panel — a tripped breaker may look partially on rather than fully off, so push it firmly to the OFF position before resetting. Also check any nearby disconnect switch. For hybrid heat-pump models, verify that both poles of the 240 V double-pole breaker are fully engaged — one half active results in the unit receiving only 120 V, which is insufficient. If the breaker trips again, contact a licensed electrician.
Why is my new Rheem gas water heater not igniting?expand_more
Common causes in a new installation include: the gas shutoff valve is closed or only partially open, air trapped in the newly installed gas line requiring several ignition attempts to purge, or the startup sequence was not completed correctly. Verify the gas supply to the home is active and the valve is fully open. For pilot-light models, multiple lighting attempts may be needed to clear air from the line. If you smell gas at any time, leave the area immediately and call your gas utility.
Why is my Rheem tankless water heater not activating?expand_more
Tankless water heaters require a minimum flow rate to activate the heating cycle — this threshold varies by model, so check your user manual. Partially closed service valves, a clogged inlet filter screen, or very low-flow fixtures can prevent activation. A plumbing crossover (where cold water backs into the hot-water line) can also confuse the flow sensor. Confirm all service valves are fully open and check the display for an error code before proceeding.
Does a brand-new Rheem water heater need to be registered?expand_more
Product registration is strongly recommended and may be required to activate full warranty coverage. Rheem typically requires registration within 60 days of installation. Registering your unit, retaining your installation invoice, and keeping your model and serial number accessible protects your warranty rights and simplifies any future service calls. Registration can usually be completed at rheem.com.
Should I call the installer or Rheem if my new unit is not working?expand_more
Contact the installer first when the unit has never worked correctly since installation. Installation errors — closed valves, incomplete wiring, improper venting, or failure to commission the unit — are the most common causes of problems in newly installed water heaters. Once an installation issue has been confirmed or ruled out, contact Rheem warranty support if a manufacturing defect is suspected. Keep your installation invoice, model number, serial number, and a clear description of the symptoms.
Can installation problems affect the Rheem warranty?expand_more
Yes. Rheem warranty coverage generally requires that the unit be installed by a qualified professional in accordance with all applicable codes and the manufacturer's installation instructions. Incorrect installation, unauthorized modifications, or use outside the intended specifications may affect or void warranty coverage. Always use a licensed plumber or HVAC contractor and retain a copy of the installation invoice as proof of professional installation.
Why does the breaker keep tripping on a new Rheem water heater?expand_more
A breaker that trips repeatedly on a new water heater usually indicates an electrical problem: the circuit may be undersized for the appliance's amperage requirements, wiring connections may be incorrect, or there may be a fault in the unit itself. Do not repeatedly reset a breaker that trips immediately. Contact the installing contractor and a licensed electrician to verify the circuit size, wiring, and connections before continuing to use the unit.
Is a new Rheem water heater covered under warranty?expand_more
Rheem offers warranty coverage on new residential water heaters, but terms vary by model series. Coverage typically includes a parts warranty and a limited tank or heat-exchanger warranty. Labour coverage under the standard warranty is generally limited to the first year. Register the unit within the required period (typically 60 days), retain your installation documentation, and verify the specific warranty terms for your exact model and serial number at rheem.com/warranties.
Sources Consulted
- [1] Rheem Manufacturing — Electric Water Heater Use & Care Manuals; startup procedures for filling before energizing. media.rheem.com (Hybrid HPWH Use & Care Manual, AP23657 Rev 01). Accessed June 2026.
- [2] watersystemwiki.com — “How to Start Your Water Heater: A Straightforward Guide for Rheem and Honeywell Models” — gas line purging on new installations. 2025.
- [3] Rheem Manufacturing — “Understanding Rheem Hybrid Electric Heat Pump Water Heater Operating Modes.” rheem.com/water-heating/articles/understanding-rheem-hybrid-electric- heat-pump-water-heater-operating-modes. Accessed June 2026.
- [4] Rheem Warranty Summary — U.S. Residential Water Heaters. rheem.com/warranties. Verify current terms for your exact model at the time of purchase.
- Natural Resources Canada — Guide to Residential Water Heaters. natural-resources.canada.ca. Accessed June 2026.
- U.S. Department of Energy — Water Heater guidance. energy.gov; ENERGY STAR product database, energystar.gov. Accessed June 2026.
Troubleshooting steps depend on the exact Rheem model. This article provides general guidance only and does not replace the official user manual for your specific unit or advice from a licensed professional. Local codes and regulations may vary.