Rheem Tankless Water Heater Will Not Power On

Rheem Tankless Water Heater will not power on or turn on due to one of the following reasons: 

• Power cord isn’t plugged in
• No voltage at the wall plug
• 3-amp fuses get blown out
• The fuse on the control board gets defective
• The heater is in maintenance mode
• Bad control board
• Issue with gas

To discover each troubleshooting step in detail, keep reading. 

Rheem Tankless Water Heater Will Not Power On [7 Easy Solutions]

Here are the culprits that cause the water heater to not turn on: 

1. Power Cord Isn’t Plugged In

Your tankless water heater won’t turn on if you don’t plug the power cord into the wall plug. Or, if the circuit breaker for the water heater is in the Off position, you can’t power on your tankless unit. 

How To Fix: 

Verify that you plug the power cord of the water heater into a properly grounded, 3-prong wall outlet. Next, go to the main circuit panel of your home and ensure the circuit breaker for the tankless water heater is On. 

2. No Voltage At the Wall Plug

If the wall plug you used to power on your water heater gets damaged, you can’t turn on your tankless unit. You can determine if the wall plug is functional. 

Plug your phone’s charger into the wall plug and see whether it’s charging up your phone. If not, understand the wall plug is at fault.

Repair the wall plug and ensure the voltage range is sufficient to power your water heater. Remember that it’s an electrical issue- not a water heater fault. 

3. 3-amp Fuses Get Blown Out

Rheem Tankless Water Heater has two 3-amp fuses. If those fuses get blown out, the unit receives no electricity to power the water heater. 

How To Fix: 

Check the fused power leads next to the junction box. Regarding this, get a digital multimeter and measure the voltage of the wires inside the junction box. 

Measure the voltage between the black and white wires next to the junction box. The voltage should be 108 – 132 VAC. If not, replace those fuses. 

4. The Fuse On the Control Board Is Bad

Rheem Electric Tankless Water Heater has a 5-amp fuse on the control board. If this fuse gets blown out, the control board will receive no electric power. As a result, the unit won’t turn on even though you press the power button on the remote control. 

How To Fix: 

Before replacing the fuse, check the fuse electrically. Measure the voltage through the fuse located on the control board. The voltage should be 100VAC. If not, I bet the fuse is bad. In this case, you should replace the PCB fuse to resolve this issue. 

5. The Heater Is In Maintenance Mode

The tankless water heater won’t turn on if it goes into maintenance mode. You must deactivate the maintenance mode if you want the water heater to work again. 

To deactivate the maintenance mode, hold down both the up and down buttons on the remote control for a few seconds. Then, turn on the water heater by pressing the power button. 

6. Bad Control Board

The control board is the brain of your tankless water heater. If it’s at fault, the unit won’t turn on. To resolve this issue, you should replace the control board. I recommend you hire a certified technician to make this replacement. 

7. Issue With Gas

If you have a gas-powered Rheem Tankless Water Heater, ensure it receives a continuous gas supply at the correct pressure. You can’t ignite the burner without a proper gas supply and pressure. 

Ensure you open the gas supply valve fully. Next, get a manometer and verify that the gas pressure is within specification. 

According to the Rheem User Manual, the inlet gas pressure should be between 4″ W.C. and 10.5″ W.C. if you power up the water heater with natural gas. On the other hand, the gas pressure range will be 8″ W.C. – 14″ W.C. if you have a water heater powered by LP gas. 

Discover More: Rheem Tankless Water Heater Troubleshooting Manual

Rheem Tankless Water Heater Remote Won’t Turn On

The UMC remote control for your Rheem Tankless Water Heater won’t turn on if there is a power outage. Besides, the UMC-117 remote control won’t turn back on if you unplug it- in some cases. 

Fortunately, you can resolve this issue simply by closing the hot and cold water valves at the bottom. Once you close those valves, press the power button. And the remote control should turn on right away. Then, turn on the hot and cold water valves again. 

How Do I Reset Rheem Tankless Water Heater?

Follow these 4 simple steps to reset your tankless water heater: 

• Turn off all the hot water faucets.
• Turn the water heater off by pressing the power button on the remote control. You can also turn off the unit at the circuit breaker.
• Wait about 5 minutes. Then, restart the tankless water heater by pressing the power button. 
• It should reset the water heater. 

Discover More: Rheem Water Heater Reset Button

End-Note

Follow every troubleshooting step I mentioned if your Rheem Tankless Water Heater will not power on. In a quick recap, I recommend you go along with these steps: 

• Ensure you plug the power cord into a properly grounded wall outlet.
• Verify the outlet is functional and has the proper voltage to power the water heater.
• Check the fuses and replace them if they get blown out.
• Check the PCB fuse and replace it if required.
• Deactivate the maintenance mode if the unit goes into this mode. 
• Ensure the unit is getting proper gas supply and verify the gas pressure is within specification. 

Besides, check the burner and ensure it’s free from obstructions. Also, don’t forget to inspect the water filter for blockage and clean the filter if needed.