Rheem Thermopile Voltage Low: 2 Red Flashes

The Short Answer: On Rheem atmospheric gas water heaters, two red flashes every three seconds means low thermopile voltage while the pilot is still lit. The thermopile, heated by the pilot, powers the gas control. If its output drops, the control can’t reliably open the main burner. Rheem’s manual points to the thermopile connection, its wires, and the pilot assembly. A technician measures the voltage and decides which part needs replacing.

What the thermopile does

Rheem’s atmospheric heaters don’t plug in. The gas control runs on the small voltage produced by a thermopile sitting in the pilot flame. A strong, steady pilot makes enough power to run the control and open the main gas valve. A weak pilot, a dirty or failing thermopile, or a poor connection lowers that voltage.

Rheem’s Use & Care manual (opens in a new tab) lists:

So two flashes is an early warning: the heater may still work, but the pilot often goes out, or the main burner stops lighting, if the cause isn’t fixed.

Common causes

• Weak or poorly shaped pilot flame, often from a partly clogged pilot orifice or a starved air supply.
• Lint or dust at the air intake at the base of the heater.
• A thermopile at the end of its life, or one damaged by heat.
• A loose or corroded connection where the thermopile plugs into the gas control, or damaged wires.
• Drafts that push the pilot flame away from the thermopile.

What you can check safely

1. Confirm it’s two red flashes repeated every three seconds, and not one blue flash.
2. Clean dust and lint from the floor around the heater and the outside of the air-intake area.
3. Look for drafts from nearby fans, open windows, or doors and reduce them if you can.
4. Look at where the thermopile wire connects to the gas control. If it’s clearly loose or damaged, tell the technician, but don’t unplug or reseat it yourself.

What the technician will check

A technician will measure thermopile output with the pilot running and compare it with the specification for your control. They inspect the pilot flame and clean or replace the pilot orifice, check the thermopile wires and connector, and look at the air intake and flame arrestor. If the pilot is good and output is still low, they replace the thermopile or the pilot assembly. On these sealed heaters that means opening the burner door, which Rheem says requires a new door gasket.

Repair or replace

A thermopile or pilot assembly is a routine, moderately priced repair on a sound tank. If the heater is old and also has a leaking tank or heavy rust, replacement may be better.

Related: Rheem water heater pilot light won’t stay lit, Rheem water heater no status light, and water heater thermocouple problems.

Frequently Asked Questions

Q: Can I keep using the heater with two flashes? A: It may keep working for a while, but it’s likely to stop as the voltage falls further. Schedule service rather than waiting for it to go cold.

Q: Is a thermopile the same as a thermocouple? A: No. A thermopile produces more voltage and powers the whole control. A thermocouple only holds a pilot safety valve open. They aren’t interchangeable.

Q: Will cleaning the thermopile fix it? A: Sometimes a better pilot flame or a cleaned air intake restores output. A technician can test before and after to see whether a new part is needed.