How to test a thermocouple tip
(United States )
I couldn't get the pilot light on my water heater to stay on no matter how long I kept the pilot light start button depressed. Following your instructions on the web, I disconnected the thermocouple and measured its voltage: 0 mV without heating and 30 mV with heating, so it looked fine.
But before replacing the whole gas control unit, I considered that the voltage might be OK but the current delivered to the regulator might not be sufficient. So, I replaced the thermocouple and voila, everything now works fine, and I only need to depress the pilot light valve for a few seconds to get the pilot light to remain on.
So, it would be worthwhile to add a section to your pilot light test info stating that one can have a good mV reading but the thermocouple is still bad. Thus, it's worth trying a new thermocouple even if the mV reading is OK, given that a thermocouple is cheap relative to replacing the whole regulator! Hope this is useful. Sure saved me a lot of money and aggravation.
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