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thelightguy · Dec 15, 2008, 11:40 PM

I've got an older Williams model Propane furnace (model # 450sfa-2) controlled by a Lux 1500 Thermostat, and I've tried everything I can think of. The Pilot lights and stays lit, but the burners will not ignite. Any help will be appreciated, it's been cold the last few days (<45 degrees... inside!:eek:) Thank you!

21boat · Dec 15, 2008, 11:59 PM

The one possibality ( if this is what you have) woud be your thermocouple. A standard gas valve has to lines. One is small line and it sends gas to the piolt spot. Now how this works is the gas sends gas to thr piolt opening and by that little flame is a thermocouple. This looks like a 1/8" copper flexable solidwire. What this does is it heats up and the actual gas valve senses and knows there is flame so the gas valve will completely turn on. Its an old saftety device so gas not lit won't fill up the house and blow things up. Np matter what you have There is the first start. I would like to know exactly what you're a to z to light and tyr to start up the furnace? And did the piolt light just blow out and this is the seasons first start up? I will look for your comeback and maybe we can narrow this down. Good luck and get warm.

thelightguy · Dec 16, 2008, 12:48 AM

Originally Posted by 21boat

The one possibality ( if this is what you have) woud be your thermocouple. A standard gas valve has to lines. One is small line and it sends gas to the piolt spot. Now how this works is the gas sends gas to thr piolt opening and by that little flame is a thermocouple. This looks like a 1/8" copper flexable solidwire. What this does is it heats up and the actual gas valve senses and knows there is flame so the gas valve will completly turn on. Its an old saftety device so gas not lit won't fill up the house and blow things up. Np matter what you have There is the first start. I would like to know exactly what your a to z to light and tyr to start up the furnace? And did the piolt light just blow out and this is the seasons first start up? I will look for your comeback and maybe we can narrow this down. Good luck and get warm.

That's what I was coming across in my research. The thermo coupler, but I had ruled it out, because wouldn't it make the pilot go out?

This is the first light of the season in a new house.
From A to Z...

I filled the propane tank, turned the valve outside on. Came inside, pressed the red button (the gas valve is an Essex, don't know if that makes a difference) for about 15-20sec, lit the pilot (I was able to do this without opening the inspection door) , turned up the thermostat (you can hear it click at the thermostat) and nothing.

I've downloaded the manual for the thermostat and checked it out, replaced the batteries and re-set it, but it seems to be working fine...

It's probably something stupid I'm over looking, but I've never had to do work with a furnace like this before, I've always used a wood stove.

Thanks for the fast reply!

21boat · Dec 16, 2008, 01:49 AM

Wood stoves are very dependable. No thermo coupler has nothing to do with the pilot lighting. That is the Pre were ready thing. The thermo coupler is the police of stop or go tp the gas valve. I am assuming the pilot light was lit for a while before you called for heat. Iam not sure of your set up but the gas valve isn't getting the get go orders. Look for any resets on a control spot. When you call for heat is the relay transfomer clicking. Boy I hope I can get you started. How old the unit?

hvac1000 · Dec 16, 2008, 05:59 AM

After you lit the pilot make sure you turned the gas valve to on instead of pilot.