Intermittent Furnace problem

[lcarter]

I have a frustrating furnace problem. The thermostat calls for heat but the furnace doesn't start. Nothing zip, nada. This does not occur everything time. It will do this maybe 25-40% of the time. Of course, when the repair man is here it starts every time. I'm to the point where I may just change out everything the can be changed out. Last year I changed the thermostat but the problem continued. Any Ideas?
Thanks,
LCarter

[Ozz]

Call me and I will try and help: 816-365-9607

[Art-n-Marge]

Great offer Ozz! As usual, you da man!!!

I posted your phone number in other RV forums... Just kidding. But I will consider putting your phone number in my private contact list... Just kidding there, too.

You are brave, and may your helpfulness be rewarded in the best that people have to offer. You've got my vote.

Would you guys post what you find?

[Ozz]

You are a good guy Art.
I thought a phone call would be better than the back and forth of the Forum.
If the furnace runs sometimes, and sometimes not even a noise... sound like a control. I would suspect the thermostat.
I would pull the thermostat, jumper the heat wires. Try cycling it 5 or 6 times, wait for an hr. then try it again, if it always works... bad thermostat.
Try killing the power to the the thermostat (and furnace) it may reset and work OK.

[lcarter]

Ozz,
I will give you a call.
Thanks Ozz

[DQDick]

Ozz, doing it off line makes sense, but when you fix it please post the result. Many of us are lurking in the background to gain information against the time we have the problem ourselves. Thanks for all you do!

[Art-n-Marge]

Ozz, clever debugging technique that I did not know. Like DQDick, I'm curious not only what was fixed but how it was debugged. Knowing these things helps understand not only how to fix things, but how things work.

[Ozz]

I spoke to lcarter, (a very nice guy) when the tech replaced his thermostat, he did not replace the control board that interfaces with it up in the A/C unit. If you have control problems like he had, you want to change the set. I think the tech was just lazy and replaced the thermostat only. I suggested he get him, or someone else back out and change the control board. Now that he has this problem, I would change the set, both new, not just add the control board with the almost new thermostat, as the board may have damaged the replacement thermostat.
As always, with an intermittent problem, it isn't easy to pin down the culprit.

[DQDick]

Thanks Ozz for the update!

[garyka]

I had the exact same thing awhile ago and it turned out to be a I had a bad connection somewhere and the serviceman suppled a new power source from another line and it's been working since(2 years)