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So I took out Kenmore Power Miser 9 burner assembly and want to root cause why the pilot light kept going off whenever I released the RESET button during ignition procedure.

Here is the test I did: enter image description here

I put the fire for 10 seconds below the thermocouple and saw that voltage ramps up only to 30mV.

I believe I was supposed to see more, like 400mV? Does this mean that thermocouple is bad?

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NO, thermocouples may operate at as low as 1-13mv (10-13 mv for operating current, 3-1mv for ECO -emergency cut-out- at low temp.).

Some older appliances used what we call thermopiles or pilot generators (which were actually a bunch of thermocouples bundled together) to supply higher current flow (like 400mv) to operate equipment and/or control circuits (gas control valves, thermostat circuits, fan control relays, etc.)

example: enter image description here

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  • Indeed, found this test on youtube - youtube.com/watch?v=6CDGmyU-e24 - which confirms what you are saying. So if my pilot light goes off whenever I release RESET button and I see voltage on thermocouple then it probably means that gas control valve is probably not functioning properly? – Hans Solo Nov 15 '18 at 4:54
  • Make sure that you do not have any other resetable limits tripped . – d.george Nov 15 '18 at 12:17
  • @d.george I suppose the problem was actually that thermocouple (when inside water heater) did not heat enough from pilot light to generate voltage. And it did not heat enough because of obstructed pilot light orifice - the flame was too small. After cleaning the pilot light orifice everything works fine. – Hans Solo Nov 15 '18 at 22:22

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