Furnace problem - not staying lit

[Afrodeziak]

I'm in a really old house with a really old furnace.

Recently discovered that the pilot light was out and after re-lighting it, it seems to be working with the furnace running.

Problem is, when the furnace stops running (reaches the temperature set on the thermostat), both the burner and pilot light extinguish.

I'm going to change the thermocouple out, as that seems to be the cheapest fix to troubleshoot, but would like any other feedback. To add, when I light the pilot and hold it on (waiting for the thermocouple to heat), it does seem to take quite a long time 30 seconds+ before the pilot will keep on by itself.
I have nothing to compare this to, whether this is normal or not.

[ercchry]

because 1945 build year and ORIGINAL furnace :rofl:

[Afrodeziak]

Don't be jealous Eric. haha

[ercchry]

of being woken up every time it kicked in? :D

[gretz]

move the pilot closer to the thermocoupler, the flame may not be hitting it enough

[Rstar]

Sometimes there is carbon build up on the thermocouple thing. You can just rub it off with steel wool and you should be good.

[tangj]

Originally posted by Rstar
Sometimes there is carbon build up on the thermocouple thing. You can just rub it off with steel wool and you should be good.

+1 Same thing happened to me

[mo_money2supe]

Originally posted by Rstar
Sometimes there is carbon build up on the thermocouple thing. You can just rub it off with steel wool and you should be good.

Same thing works for me, but only for a short while. After only a few days though, especially on the cold wintery nights, it just seems to not ignite again. *Subscribed hoping for more info*

[SJW]

A new thermocouple is like 7 bucks. Just replace it.

[redrocket]

Swapping the thermocouple is worth a try and very cheap but i dont figure it will fix the problem your having with the pilot going off. It would fix it if the problem was your burners turn on for a short time then stop, the thermocouple is used as a " flame proofing switch" to make sure there is actually fire and it's not just pumping gas into the furnace And is primarily for the burners not the pilot. I have not dealt with a furnace that old before but what you could try is there is a sensor inside the "plenum" basically Inside the furnace that is designed to shut off the burners and pilot light when it gets to hot to prevent it getting so hot it could Cause a fire this may be faulty. And I can't imagine the sensors being pricey Now again I've never worked with as old of a furnace as you are talking but to give you a Idea of the normal operation and maybe you can see what operation is not happening on your furnace you can check these videos

http://www.google.ca/search?q=troubleshooting+furnace+order+of+operation%3F&hl=en&safe=off&client=safari&prmd=imvns&source=univ&tbm=vid&tbo=u&sa=X&ei=pPNsULjuKqnriwKz_IGIBQ&ved=0CDAQqwQ&biw=320&bih=416

I clicked the Sequence of operation for 80% furnace but with some search sure you can find a older furnace. Hope it some help I'm not a furnace guy just brushed up on it in electrical school and in my own house.

[Afrodeziak]

I took some fine grit sand paper to the thermocouple and igniter, got rid of some of the white "ash coating."

Also took some isopropyl and a rag and wiped it all down for good measure, then took a compressor and blue some air at it.

Has been up running for the last few days.

Guess I'll see how long it goes for.