The Rheem Manufacturing Company produces a line of water heaters, air conditioners and furnaces for both homes and businesses. A flame sensor detects heat coming from the burners. This is a safety mechanism. A burner with no flame may release gas into the air. When the sensor becomes blocked with debris, the heater will not work properly. It will shut down the unit even if it is producing heat. Cleaning the flame sensor is basic maintenance that will improve the functioning of your Rheem heater.
Turn off the power supply to your heater at the breaker box. Turn off the gas feed going to the heater.
Remove the lower front panel from the heater to access the burners. The design of Rheem models will vary. For many heaters, you unscrew a panel with a screwdriver and lift it off.
Pull out the flame sensor once you locate it. Look near the burners for a rod with a ceramic base. There will be a wire that attaches it to the heater. Unscrew the bracket holding the sensor in place and unhook the wire. Pay attention to how it is connected to the heater so you can reattach it.
Wipe the surface of the flame sensor down with 400-grit sandpaper. This will remove stuck on soot and debris. Clean off the dust with a rag.
Reinstall the flame sensor reversing the steps you took to remove it. Place it in the bracket and tighten the screws. Reattach the wire to the heater.
Turn the power and gas back on to the unit and test it. A dirty sensor will cause the heater to shut down over and over. If the problem is the flame sensor, the heater should kick on and stay running.