Furnace question

[Jeff Monson]

So I've got an older natural gas furnace in my woodshop. Carrier is the brand and I'm not sure of the year built, but its not a high efficiency model (15 to 20 years old??). Anyway the furnace goes out about once a week or so, the pilot light is out when I inspect it. Relight the pilot light and it works great for a few days or more. Anyone out there to offer me some advice on what to look for as the problem?

[Mark Bolton]

Bad thermocouple? Other than that it would likely only be a stiff breeze blowing the pilot out. This would normally only happen if you opened big doors or had major air flow and it likely wouldnt be something to "pop up". I would try the thermocouple first.

Mark

[Mark Bolton]

Should have also noted, to check your pilot and make sure the flame is making good contact with the thermocouple tip and the tip is clean. Sometimes the orifice in the pilot nozzle can get plugged causing a weak flame. You can disassemble the pilot tip and blow it out with air. Just dont use a wire or anything to try to poke it out as there is a small orifice in there that if scratched will not work well.

Other than the thermocouple, plugged orifice, the only other thing would be a failing gas valve (main part where your knob is that you push to light the pilot)

Mark

[Matt Meiser]

If the thermocouple is dirty, try scraping with the edge of a knife to clean it. I've had to do that a few times on the thermocouple on our camper's hot water heater. Then order a new one because its probably only a temporary fix.

[Jim Koepke]

Another possible problem with a thermocouple is the mounting hardware can become loose over time. This can cause a thermocouple to stop working.

For a thermocouple to produce its small amount of current there has to be a hot end and a cool end. If the screw or hardware holding the cool end becomes loose, it can not sink off the heat. If it can't sink off the heat, it can't make electricity.

jtk

[Jeff Monson]

Thanks for the quick replies, the thermocouple is the probe that makes contact with the pilot light correct??

[Matt Meiser]

Yes, that's it. If it doesn't detect the heat from the pilot, it shuts off the gas as a safety measure. A HVAC tech who came to fix ours told me that the oxidation that builds up on them messes with the reading. He's the one who told me the knife trick.

[Ken Fitzgerald]

I paid $85 recently for a HVAC technician to scrape the thermocoupler on our home heating furnace.

[mickey cassiba]

I paid $85 recently for a HVAC technician to scrape the thermocoupler on our home heating furnace.

Ken...call me. I'll scrape it for $20. But you'll have to to pay per deim, etc.

[mickey cassiba]

Actually, I have the same problem. We live in a high wind area, and occasionally the pilot goes out. It's a 1960 unit. The wind gusts do blow out the pilot flame. Right down through the exhaust pipe. Fortunately, we only use it about 20 days per year.

[Ken Fitzgerald]

Ken...call me. I'll scrape it for $20. But you'll have to to pay per deim, etc.

I suppose for $20 you'll want me to pay for airplane tickets too?

[Rick Potter]

Thermocouple is best bet, but I am just wondering if you have a big dust collector that might be sucking air down the vent and blowing out the pilot?

Rick Potter

[Charlie Reals]

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

[Al Willits]

$85 to scrape a TC lead???
Considering how cheap they are I'd find a new tech, not very professional imho.

If he lights the pilot that leaves out electronic ignition, like said the pilot or TC would be my first choice, considering the cost of a meter to measure millivolts I'd just replace the TC lead and make sure the pilot was sharp, and blue in color, lots of yellow in the pilot flame means somethings wrong with it.

Problem with diagnosing something like a furnace over the web, is you can get into a lot of trouble, do the basic checks and if that doesn't work, call somebody.

Al

[Matt Meiser]

$85 to scrape a TC lead???
Considering how cheap they are I'd find a new tech, not very professional imho.

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