Pilot light on Water Heater

[jerry d]

About 2 years ago i replaced the H2O Heater with a new unit.(gas only). It worked perfectly for the first 20 months.
Now I light the pilot, the heater comes on, may work perfectly for 1 or 2 days, or 10 or 15 minutes. I have replaced the thermocouple, yet the problem persists.
The last time I filled the propane tanks I noticed that there was liquid in the tanks (condensation) even though the gas was clearly empty.
The propane dealer vented the tanks while re-filling the tanks and forced some moisture out.
Could moisture in the propane tanks cause the problems with my water heater?

[HowieE]

If there was water in your tank the only way to get it out would be remove the valve and drain it.

Propane comes out of the tank as a vapor, of the top of the tank.
The first thing I would suspect would be a weak pilot and being blown out by the wind. Look at the size and color of the flame. It should be blue not yellow.

[jerry d]

The pilot flame is blue, and that is correct about the gas as a vapor, just don't know why sometimes this will work perfectly and sometimes not.
I thought it was the wind, however very often, this will happen when dead calm. Sometimes 5 minutes after I light the water heater the flame goes out, and also the pilot flame. Some evenings I may have to relight the heater 2 or 3 times. Sometimes it will work fine on one light and stay lit for the rest of the night. Its becoming annoying.

[Jammer]

Hi Jerry

In sequence:

1) Clean the pilot and thermocouple assembly
2) Disconnect the thermocouple from the gas valve and clean the connection (both sides). Reinstall with the proper torque
3) If there's still a problem, check the thermocouple with a voltmeter with a millivolt range. Should be 25-30 millivolts. If less than that adjust the thermocouple so it's properly positioned in the pilot flame or replace it. You will have to disconnect the thermocouple to connect a meter. Have an assistant hold down the valve
4) If the thermocouple checks out OK then replace the gas valve

[drboyd]

You might also want to make sure that the pilot flame stays in contact with the thermocouple after the main flame starts. I've seen issues where the draft from the main burner will suck the pilot flame away from the thermocouple. Look for a loose or missing cover.