Gas and Oil Home Heating Furnaces - Janitrol gas furnace won't light

I have a janitrol gas furnace which I bought new 7 - 10 years ago. Last year I had problems with the pilot going out in the middle of the night if I had the thermostat set low. (If I had it on 70 it stayed lit). I dealt with relighting the pilot all last year.
Over the winter the pilot stayed lit. When I turned the thermostat on this year the blower motor comes on but the burner does not light. The furnace will blow cold air indefinately. The pilot however stays lit.
Can someone suggest a possible solution for me to try? I am on a tight buget and can't really afford a repair man.
Thanks in advance, -Bob

Is this a free standing pilot light? (Stays on all times)

If it is, you may have to go to Home Depot, or hardware store, and buy a new Thermocouple.

Make sure the pilot asembly is clean as well.

Also check for 24v at the gas valve on a call for heat.

Does the thermocouple have anything to do with the burner lighting or just the pilot? I have one but never put it in. I'll check the voltage at the fuel valve tomorrow. It's getting cold here, nothing like waiting to the last minute.
Thanks, -Bob

On a furnace the age of yours a bad t-couple will kill the pilot also.

If you've got a meter 1st just check and see if you have 24v out of the transformer. If you do jumper R - W and see what happens. If nothing confirm there is 24v at the gas valve. If you don't check your safeties.

i have a janitrol central heat and air unit that is probably 20 yrs old. ive replaced the thermal coupler but the pilot light will not stay lit. i dont know what else to do. please help.

ive replaced the thermal coupler but the pilot light will not stay lit.

Make sure the nut into the gas valve is tight and make sure about 1/2 the t-couple is in the pilots flame.

While you are holding down the gas valve button for the pilot and you've got it lit, what does the flame look like? Is it a pretty strong blue flame??

if the tcouple is properly in the flame, and pilot does not stay lit, replace tcouple first, if still persists, valve most likely, i have seen many fail in this way

I would like to thank everyone for their ideas. Let me sum up what I have to date.

It is a Janitrol GUPS100-3 furnace

I was having a problem with the pilot staying lit but it is fine now, been lit since last winter.

The thermostat works, and when turned up the furnace fan comes on but the burner does not light.

I do not have power to the gas valve

There is a circuit board with a transformer that has 110V to it.

I have no voltage across the fuse in the circuit board

Hope this helps with your diagnosing, -Bob

I have no voltage across the fuse in the circuit board
Have you put a new one in????

ED ;)

Fuse appears to be good but I jumped accross it just to make sure.
-Bob

Just check for voltage right off the transformer. You should have 24v. If not the transformers bad.

There are many wires attached to the transformer. Which ones do I test? If the circuit board is bad will the transformer still have voltage out? -Bob

I am slowly becomong an expert on replacing parts but still have no heat. Since I now have a little bit more knowlege I'll start from scratch.

I have a constant pilot light. I turn on the thermostat and the small fan comes on, (not the fan that circulated the heat throughout the house), but the burner does not light. There is no voltage to the gas valve.

Since my last post I have replaced the circuit board and the transformer but still have no heat. I'm running out of patience and it is getting cold. Any ideas?

Do you have an air proover switch there? When the little fan comes on it has to proove and if it's not the burners wont light. I'm guessing this is a 80% furnace with a metal flue pipe?? I've seen where these were installed right into the old chimney with no flue liner and birds have made their way down the flue and clogged it.

I disconnected the flew pipe at the furnace fan. Still nothing. I experimented with partially putting the pipe back on in case there had to be some back pressure but still nothing. The diaphram that connects to the fan in question with a vacuum hose, is it a safty device that can be bypassed for testing?

Thanks in advance,
-Bob

You can jump it for testing only. If it's not closing you need to determine why. It could just be a bad switch though.

I wish I had read this sooner. You can check the diaphragm switch by setting the system to heat. The liitle inducer fan will start. If the little inducer fan starts, the stat is good, and the transformer is good, the fuse is good, and the board is good. Pull the hose off the inducer fan and lightly suck on it. Try to keep it constant. This will close the diaphragm switch. All these switches have to close "in order" or it won't work, the board senses it. If the pilot and burners light, We need to know what color the inducer fan is? If it is all black, then the paint internally has crystalized from the heat over the years and has changed the vacuum the fan can pull. It just won't close the internal (other end of the hose) switch anymore. Most manufacturers are aware of this problem and have repair kits available. Let me know. :cool:

I tried sucking on the hose and nothing happened. However, I bypassed the vacuum chamber and walah!, HEAT!!!!!! Now what do I do, replace the vacuum switch? Thanks for all of your help, -Bob

if you are sure flue pipe is clear, check tubing for holes, if all good replace switch