Furnace question

[Lee Schierer]

On a furnace that old, the thermocouple is likely not electronic. It is likely that it is a capillary tube type. In my experience they either work or don't work. They don't work intermittently. I would suspect a weak pilot flame or a back draft blowing out the flame. If a building is tightly sealed, just opening the door can cause enough back draft to blow out the pilot light if the stack is the only opening into the room. The same is true of a leaky building. Wind gusts can blow out the pilot light. A missing baffle can also cause the problem, you know that little sheet metal piece that you have to remove to relight it that you didn't bother to put back in place because it was a pain to get out and a pain to put back.

[Ben Franz]

I had a similar problem with a gas water heater 15-20 years ago. It was a fairly new one that started acting like Jeff's FAU out of the blue. When the gas utility came out to look at it, they discovered that the gas pressure regulator on the meter wasn't working properly. After replacing it, the problem went away. Just something else to look at if the more likely causes don't pan out.

[Charlie Reals]

I had a similar problem with a gas water heater 15-20 years ago. It was a fairly new one that started acting like Jeff's FAU out of the blue. When the gas utility came out to look at it, they discovered that the gas pressure regulator on the meter wasn't working properly. After replacing it, the problem went away. Just something else to look at if the more likely causes don't pan out.

Kudos thank you and praise Ben. Many things can cause the problem and not be the unit itself. I retired from the Gas utility,as a gas serviceman. We did not repair, we diagnosed with no conflict of interest. There was no charge for our service, still isn't with that company. I do not claim to be an expert, especially with today's electronic ignition though I can take ya back to the days of a Mckorkel 3way gas valve with a ladder pilot in a converted oil burner. Oh those could hurt ya if you didn't watch it
Another that comes to mind is what fuel is being used. Propane has a far different characteristic than NG.
The normal service charge here is $125 but better than some alternatives lol. I think Ken was being facetious

[Jim Koepke]

Will have to say this is the funniest thread I have read in the ot forum. Although all of the above can and for the most part is decent advise,,,,, No one bothered to ask what type of furnace it is. Carrier made and still makes several types. Being that old and taking for granted it is a FAF it might not have a thermocouple. It might have a thermopile in which case it could be a pg1 or a pg9. only one of those can be cleaned.

A dirty thermocouple is the #1 problem butt a cracked plenum chamber can also cause it. Scraping a thermocouple is only a stop gap if you don't have a new one, It will leave you cold when you need it most.. It's all good though since I got many a good laugh when called to fix what the old man screwed up listening to his buddies. Do you have the owners manual?

Out here PG&E will do a free inspection, most utilities now have a small charge.It might be worth it on that old of a unit.
m2c

If a technician will show up for free, that is your best choice.

As one person mentioned, there could be something in the pilot nozzle that is messing with the flame.

But there are so many little things that could be a problem that may not occur to those of us who have dealt with similar problems.

Too big a pilot flame can be just as bad as too weak a flame.

A kink in the lead from some thermocouples can cause a problem that would be unnoticed to those who do not know to look for it.

jtk

[Chris Kennedy]

We had a similar problem with our furnace, and it was a downdraft problem. It would just go out from time to time when the wind was just right.

[Al Willits]

That's about what you'd pay for an emergency service call around here. More if its after hours/holiday/weekend.

Wasn't the charge of $85, it was the fact all he did was scrape the TC lead, replacing it with a new one would have been only a few dollars more and a much more professional repair.

Al