furnance repair

[thunderstruck]

I cannot get my furnance to light, I have replaced the thermocouple, but the pilot will not stay lit, even though it is very easy to light, what should I do and what am I missing.

[PaPaPeng]

Press down the Pilot Light button setting to keep the pilot light lit for half a minute or more. The thremocouple has to be warmed up before it will generate a strong enough signal to keep the gas valve open. Once the pilot light stays on turn the gas valve setting to ON.

[Bob]

I've seen this problem when the pilot light jet was partially plugged. Cleaning it with a fine strand of wire solved the problem.

Bob

[thunderstruck]

I tried that, held it for two minutes, but the pilot will still not stay lit, I got it to light once but the thermocouple was not bolted down, after I bolted it down it would light but would not stay.

[Donald Gares]

Make sure that when you bolt the thermocouple down that you are NOT moving it out of the direct pilot flame.

Don

[Olaf]

Do not discount the possibility that the gas control valve may be faulty. Last year I went through about 10 or so thermocouples before i just got sick of replacing thermocouples and changed the gas control valve...... to an auto-ignition intermittent pilot system (very nice).

[PaPaPeng]

The last time I had the problem was years ago and can't remember too much else. Since you said the furnace did light once then the equipment is probably OK. The remaining suggestion is to see if the pilot light is always directed on the tip of the thermocouple. My dim memory of the last fix was that I had to fiddle with the thermocouple mount (adjust mounting screw, bend the clip??) to bring the tip onto the hottest part of the pilot light flame, the part just above the blue cone as per high school lab description. Also use steelwool or emery paper to clean the soot off the tip of the thermocouple. Soot is heat insulating and may give a false reading. Maybe clean up the original thermocouple and try relighting with that.

My house is 25 years old and at the time of its construction we had to (new rule) put in an independent air source for the furnace combustion air. I made a box duct to channel the outside air source direct to the combustion inlet as an open duct from the outside was pouring very cold air into the basement. Most people just stuffed up the pipe with insulation. During high winds the gusts would blow out pilot light. I placed a small sheet of metal to act as a baffle between the box duct outlet and the pilot light. Works like a charm and that's for more than 10 years by now.

[Stormin Mormon]

The pilot flame should be about an inch tall, and should touch the thermocouple.

[TURTLE]

This is Turtle.

Sounds like the Gas valve being bad but you can have a problem where the thermocouple screws down into the valve. There maybe two wires coming to the point where the thermocouple into the valve at and these two wires goes to a shut down on the furnace where the go to the furnace wall. these is a shut down switch at this point and can be the problem. Check it out.

TURTLE