Wow this forum does have professional discussions! I hope you guys can help me with this puzzle...( I read https://forum.heatinghelp.com/discussion/160527/gas-heating-gas-valve-or-circuit-board and it's kinda similar to my case but not exactly).
Now I look back I realized it's been 1-2 weeks sub-normal, till one morning I woke up to 5 degrees lower than my setting. Cleaned the flame sensor and it seemed improved but not a lot. Currently my observation is this:
1. The gas valve fails to turn on about half of the times;
2. The gas valve stays on when it should most of the time -- the flame sensor LED is always nice and bright, no low sensor signal ;
3. The best part: The probes of a multimeter on the gas valve terminals help tremendously to "jump" it on when it should. But only when the meter is on( I get AC 22.6-23.2v). If the meter is off, it doesn't help.
So the meter acts like a resistor? The gas valve inside has deteriorated and there is some kind of short so the board tripped it from some over-current protection(Is there such a thing for gas valve at all?) but with the meter as a resistor the protection didn't kick in? Or on the control board there is some hair-thin short that triggers the trip? I'm trying to make sense of this to decide if I should replace this 2-year-old board or have someone professional to replace the gas valve -- all wearing masks of course :).
4. I tried "Abracadabra"'s putting-fingers-on magic. I feel the relay click but not the valve tap(for the failed cases). However, for such case the voltage when the relay clicks goes down to 0 while the normal off condition is 0.8v -- that's why I was thinking of some short-circuit. Or is it a bad relay that instead of clicking to 24v it sometimes decides to click to 0v? LOL
5. If I have not confused you enough, here are what I hear for a successful cycle:
click and the small fan is on; seconds later click and igniter turns orange slowly; 15 seconds click( a big relay), tap(gas valve), and fire simultaneously, meter AC 23v steady, click of igniter off, blower's scary clicks and hot air blowing.
And a failed cycle:
click and the small fan is on; seconds later click and igniter turns orange slowly; 15 seconds click( the big relay), voltage falls from 0.8v to 0, 2 clicks(one turns off igniter one turns off gas valve I think), and try again.
I'm going to unplug the gas valve to measure the board side 24v and the valve side ohm tomorrow as suggested by "ratio" in the post mentioned above-- don't want to unplug anything now it's a snowy night and kids in bed.
Thanks for any tips!
-Jane
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