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The voltage generated by the thermopile is not related to the gas valve. Thermopiles generate electricity by maintaining a cold junction. This is the part of the device that should not be touched by a flame
Only the top ~1/4 of the thermopile should be in the pilot flame
Yep, it's installed correctly.
if the thermopile is heated when the main burners come on then the voltage output will drop
The voltage drops from ~0.3V at the gas valve to ~.15V and then slowly drops to ~0.050V and shuts down. Maybe the thermopile is set too high ?
if the cold junction (bottom 1/2 to 3/4's of the thermopile) is heated the voltage output will drop
OK, sounds like I installed the thermopile at the wrong height.
This is the only likely explanation for the symptoms you describe
Sounds good, you might have saved me $150!!! Have a happy new year!