You’ve just returned from vacation, replaced your old unit, or completed routine maintenance, and now you need hot water again. The problem is that turning on a Rheem water heater the wrong way can cause electrical shock, gas leaks, or permanent damage to the system. The startup process also differs significantly between electric and gas models, and skipping a single step can leave you with cold showers for hours.
This guide walks you through exactly how to turn on a Rheem water heater using verified technical procedures. You will learn how to restore power or ignite the pilot, set the correct temperature, verify operation, and fix common startup problems. No guesswork is required.
Confirm Safety Before Starting
Before touching any controls, take these critical safety steps to protect yourself and your equipment.
Cut Power for Electric Models
For electric Rheem heaters, always switch off the dedicated circuit breaker before any inspection. Flip the breaker labeled “Water Heater” to the Off position and wait 3 to 5 minutes. This allows residual electricity to clear and prevents shock when you access the thermostats.
Verify Gas Supply for Gas Models
On gas units, check that the gas shutoff valve handle sits parallel to the gas line. This position means the valve is open. If the handle is perpendicular to the pipe, rotate it 90 degrees. Never force the valve.
Read Your Specific Model Manual
Rheem manufactures tank, tankless, and hybrid models with slight procedural variations. Find your model number on the side label and consult the official manual for exact instructions.
Call a Professional If Unsure
If you smell gas, notice leaks, or feel uncertain about working with electricity or gas lines, stop immediately and contact a licensed plumber or electrician.
Turn On an Electric Rheem Water Heater
Electric Rheem models use internal heating elements controlled by thermostats. Follow these steps to safely restore power and heat your water.
Restore Power at the Breaker Box
- Go to your home’s electrical panel.
- Find the double-pole breaker labeled “Water Heater” or “Hot Water.”
- Confirm it sits fully in the Off position.
- Wait 3 to 5 minutes, then flip it firmly to On.
You should hear a distinct click that confirms power restoration.
⚠️ Warning: If the breaker trips immediately after you turn it on, do not reset it again. A repeated trip signals a short circuit, a failed heating element, or a wiring fault. Call an electrician.
Set the Thermostat Temperature
- Remove the access panels on the side of the heater.
- Pull back the insulation to expose the thermostats.
- Use a screwdriver to adjust both upper and lower thermostats to between 120°F and 140°F (49°C to 60°C).
- Replace the insulation and secure the panels.
The 120°F setting reduces scald risk for households with children. The 140°F setting helps kill bacteria like Legionella but increases burn risk.
✅ Pro Tip: If the heater does not respond, reset each thermostat by turning the dial to Off, waiting 10 seconds, then setting it back to your desired temperature.
Wait for the Water to Heat
After power returns, the heating elements begin warming the tank.
- Typical heat-up time ranges from 30 minutes to 2 hours.
- Larger tanks over 50 gallons or cold groundwater require the longer end of this range.
Test the Hot Water Flow
- Turn on a hot water tap at your kitchen or bathroom sink.
- Let the water run for 1 to 2 minutes.
- If the water warms up, your heater is active and working correctly.
🔍 Visual Cue: No lights, sounds, or warmth after 2 hours may indicate a tripped breaker, a failed thermostat, or a bad heating element.
Ignite a Gas Rheem Water Heater
Gas Rheem models use either a manual pilot light or electronic ignition. The startup process varies by ignition type.
Light a Manual Pilot (Older Models)
This method appears on standard-efficiency gas tanks and requires manual flame ignition.
Set the Knob to Pilot Mode
- Locate the gas control knob on the front access panel.
- Turn it from Off to Pilot.
Ignite the Pilot
- Press and hold the knob down to release gas to the pilot tube.
- While holding the knob, use a long lighter or match to ignite the pilot at the burner assembly.
- Keep the knob pressed for 30 to 60 seconds after the flame lights. This heats the thermocouple, a safety sensor that keeps the gas valve open.
Turn to the On Position
- Slowly release the knob. If the pilot stays lit, rotate it to On.
- The main burner will ignite automatically when hot water is demanded.
❌ If the pilot goes out: Repeat the process. A common cause is insufficient hold time, so make sure you press the knob for a full 60 seconds.
Activate Electronic Ignition (Newer Models)
High-efficiency Rheem gas heaters use automatic ignition, so you will not need matches.
Check Power and Gas
Confirm the gas valve sits parallel to the pipe and that electrical power is on if your unit has a digital control board or fan.
Press the Ignition Button
- Find the “Ignite” or “Spark” button on the control module.
- Press and hold it for 5 to 10 seconds.
- Listen for clicking as the electrode sparks.
- The pilot should light automatically.
Release and Confirm
Hold the button until the flame stabilizes. Clicking stops or an LED stays solid to signal success.
✅ Success Signal: A steady blue flame at the burner assembly means the system is live.
Troubleshoot a Failed Startup
If your Rheem heater will not turn on or produce hot water, work through these common issues.
No Hot Water After 2 Hours
- Tripped circuit breaker: Reset the breaker. If it trips again, call an electrician.
- Thermostats set too low: Adjust both upper and lower thermostats to 120°F to 140°F.
- Failed heating elements: These require professional testing and replacement.
Pilot Light Will Not Stay Lit
- Faulty thermocouple: Replace the thermocouple, an inexpensive part that commonly fails.
- Insufficient hold time: Hold the pilot knob for a full 60 seconds after lighting.
- Blocked pilot tube: Clean it gently with compressed air or a needle after turning off the gas.
- Low gas pressure: Contact your utility provider or a plumber.
Breaker Trips Repeatedly
Do not keep resetting the breaker. Likely causes include shorted wiring, a water-damaged thermostat, or a failed heating element. Turn off power and call a licensed electrician.
Water Heater Is Leaking
🛑 Emergency Protocol:
1. Turn off the cold water supply valve.
2. Shut off the gas valve for gas models.
3. Flip the circuit breaker to Off for electric models.
4. Call a professional immediately, since leaks can signal tank failure.
Optimize Temperature and Performance
Once your heater runs, fine-tune the settings for safety, efficiency, and longevity.
Set the Ideal Water Temperature
- 120°F (49°C): Recommended by the U.S. Department of Energy for most homes. This setting reduces scalding risk and cuts energy use.
- 140°F (60°C): Use this only if you have a dishwasher without a booster heater or need to combat bacterial growth. Install anti-scald valves at fixtures.
Verify Temperature at the Tap
- Let hot water run for 2 minutes.
- Fill a glass and use a thermometer.
- Adjust the thermostat up or down in 5°F increments until you reach your target.
🔧 Note: Thermostats drift over time, so recalibrate annually.
Maintain Your Rheem Water Heater
A properly maintained water heater lasts 8 to 12 years and operates efficiently.
Flush the Tank Annually
Sediment buildup reduces efficiency and can cause overheating.
- Turn off power and the water supply.
- Attach a garden hose to the drain valve.
- Open the valve and let water flow into a bucket or floor drain.
- Flush until the water runs clear.
- Close the valve, refill the tank, then restore power.
Test the Pressure Relief Valve
This safety valve prevents tank explosion from overpressure.
- Lift the lever halfway, then release it.
- Water should gush out briefly, then stop.
- Replace the valve if it leaks continuously or fails to discharge.
Inspect for Corrosion and Leaks
Check pipe connections, the drain valve, and the anode rod. Replace the anode rod every 3 to 5 years.
Frequently Asked Questions About Rheem Water Heaters
How long does it take for a Rheem water heater to heat up after turning it on?
Electric Rheem water heaters typically take 30 minutes to 2 hours to heat a full tank. Gas models generally heat faster, though exact recovery time depends on the BTU rating and tank size.
What temperature should I set my Rheem water heater to?
Set your Rheem water heater between 120°F and 140°F. The 120°F setting reduces scald risk and saves energy, while 140°F helps control bacterial growth but increases burn risk.
Why is my Rheem water heater pilot light not staying lit?
The most common causes are a faulty thermocouple, insufficient hold time during ignition, a blocked pilot tube, or low gas pressure. Hold the pilot knob for a full 60 seconds after lighting, and replace the thermocouple if the problem persists.
Can I turn on my Rheem water heater myself, or should I hire a professional?
Most homeowners can safely turn on a Rheem water heater by following the correct steps for their model type. However, contact a licensed plumber or electrician if you smell gas, see leaks, or feel unsure about working with electrical or gas connections.
What should I do if my circuit breaker keeps tripping after turning on the water heater?
Stop resetting the breaker immediately. Repeated tripping signals a short circuit, a failed heating element, or water intrusion. Turn off power and call a licensed electrician to diagnose the problem.
How often should I flush my Rheem water heater?
Flush your Rheem water heater once a year to remove sediment buildup. This routine maintenance extends the unit’s lifespan and maintains heating efficiency.
Key Takeaways for Turning On a Rheem Water Heater
Turning on a Rheem water heater is straightforward when you follow the right steps for your model type.
- Electric models require a breaker reset, thermostat adjustment to 120°F to 140°F, and a 30-minute to 2-hour wait.
- Gas models with a manual pilot require holding the knob for 60 seconds after lighting.
- Gas models with electronic ignition require pressing and holding the ignite button.
- Common startup failures include tripped breakers, low thermostat settings, and faulty thermocouples.
- Leaks or repeated breaker trips require immediate professional help.
Always prioritize safety. When in doubt, consult your Rheem user manual or a licensed technician. A few minutes of caution can prevent costly repairs or dangerous accidents.
Now that your water heater is running, enjoy the comfort of reliable hot water, knowing you did it right.
