Propane water heater won't stay lit

Question

My water heater is 3 years old and a I've never had an issue with it until recently. It just won't stay lit. It goes out within seconds.

I replaced the thermocouple and did the soapy water test to make sure there were no leaks and that went well but it's still not staying lit.

I do have really hard water (well water, no water softener because there's not room for one) so I'm not sure if that would affect anything. Really appreciate any insight into what to look into next to fix it.

Water heater is a Richmond, model number 6G30-30PF3 if that matters

Answer 1

Usually it is the thermocouple, but since you replaced it lets assume it is something else.

The thermocouple has to deliver a signal of >200 mV for valve to stay on, measure that.

Next to check is the exhaust sensor or the Upper Limit sensor.