Water heater pilot not staying lit

Question

A customers 70 gallon gas fueled Bradford White water heaters' pilot light goes out immediately after releasing the red pilot button when relighting it. I concluded (in order of most likely suspects) the thermocouple which was replaced. No change. I figured next it could be a clogged orifice (not likely), but pulled the burner anyway to clear the tube. No clogs and no change. Gas supply is strong. No blockage in the exhaust vent.

This is a model that is 8 years old. It's most likely past the its' life expectancy. The customer has left the decision to repair or replace up to me. A similar model will cost $1200 plus my labor to replace. If I wanted to repair it and wanted to order a part would I be correct in assuming that the thermostat valve is what's preventing the pilot from staying lit? I will most likely replace the unit, but would like to know if my guess about the repair is correct?

Answer 1

You should test the output of the thermocouple with a multi-meter to confirm that the replacement is working as expected.

An 8-year old heater would have an "auto-reset" thermal cut-off switch built into the pilot assembly, to protect the burner compartment from overheating, these can go bad. Was that replaced when the thermocouple was replaced? For modern heaters it is recommended to replace the entire pilot assembly, not just the thermocouple.

You should be able to purchase a replacement gas control unit for significantly less than a new heater. My heater is 16 years old and still going strong, 8 years is not necessarily "end of life".

Check out this tutorial : Water Heater Service Training