Rheem / Ruud / Richmond atmospheric gas tank with electronic thermopile control: quick sheet (diagnostic and electrical side)

The pilot burns continuously and heats a thermopile, which produces a DC millivolt signal. That millivolt power runs the electronic gas control: it holds the pilot valve open, powers the status LED and opens the main burner valve when the tank calls for heat. No pilot means no power, so a dark LED usually just means the pilot is out.

A temperature sensor in a well that reaches into the tank reports water temperature to the control. When the water drops below the knob setting, the control opens the main valve and the pilot lights the burner. The control also contains a high-limit (energy cut-off) function that shuts the gas off if the water gets far too hot and reports it as 4 blinks.

The FVIR (flammable vapor ignition resistant) chamber is sealed. Combustion air enters through a flame arrestor so that vapors from spilled gasoline or solvents cannot be ignited outside the chamber. Rheem's Guardian design also adds an air shut-off: a thermal release device closes off combustion air (and the control shuts the gas) if the chamber overheats. A tripped thermal device means the chamber ran abnormally hot and must be investigated by a gas technician; Rheem publishes a bulletin for replacing it on Guardian models.

On the water side, cold water enters through a dip tube that carries it to the bottom of the tank; hot water leaves from the top. A magnesium anode protects the glass-lined steel tank. On many models the anode sits in its own hex-head port on top; on some it is built onto the hot outlet nipple. A T&P relief valve protects against excess pressure and temperature, and a drain valve at the bottom is used for flushing sediment.