View Full Version : Gas Furnace: Main Burner not coming on

02-29-2004, 02:18 PM
Hi Everyone...

I have an older (15 years or so) GE 120,000 BTU forced hot air Natural Gas Furnace. Starting this morning the Main Burner doesn't seem to want to come on. This is a furnace with a continuously lit pilot, and that's working fine.

I have a small manual on the Honeywell Gas Control that says I should check the Valve Operator. Only I have no idea what the hell that is...

So should I just go and get a whole new gas Control, or what's the best way to fix this.

We do have a small Direct Vent Gas Stove, so the house isn't too cold, but if the temp drops it will get chilly.

I suppose at some point I should be looking to get a new furnace installed. Maybe now is the time...



Gary E
02-29-2004, 02:55 PM

15 yrs is not old, and can be repaired very easy by a qualified mechanic. Heating systems are not that complicated and someone you know may know what to do, this is time to phone a friend for help or a recomendation of a heating contractor that wont rip you off. Please do not mess with gas if you do not know how the system works.


Del Lansing
02-29-2004, 03:18 PM
Look for loose, disconnected wires at the gas control valve (where the on/off/pilot knob is) and the wires that connect the overlimit switch (higher up on the plenum, looks like a dial thermometer with 2 sometimes three pointers)
Of course nobody bumped the thermostat into "off" did they?

02-29-2004, 04:44 PM
Had the same problem last November, where the heater would go through all the motions of lighting, then not light. This was pretty much a sudden occurance; one day it worked, the next it didn't. Turned out to be a bad solenoid that controlled the gas delivery valve. It just takes a guy with a multi-tester and knoledge to wield it to find out if this is the problem, and then you will need a new one installed if it is.

Of course, this happened to me the week before I finished installing my new oil-fired heating system (my gas heating bill was outrageous). Musta had bad karma somewhere @*!&$#!


02-29-2004, 04:59 PM
Well, something is wrong, and I don't really know where to begin with this system. It's so simple, and yet without a starting point I can't really figure it out. I'm very surprised that there aren't websites devoted to this kind of thing.

It looks like I will be calling in a heating repairperson to come take a look and see what they can do.


[ 02-29-2004, 06:00 PM: Message edited by: Noah ]

Paul Scheuer
02-29-2004, 05:28 PM
It may not be a simple as it looks. The time to understand it is before it fails. There are parts that are designed to fail safe. It may be possible to get it running by bypassing some of those protective devices. Not a good thing. Somewhere there is an overlimit thermostat that is supposed to turn the furnace off if it runs away. There is also a "proof of flame" device. Either of these can indicate, properly or not, that it's time to turn off the gas. You'll sleep better knowing that a pro has checked these things out.

02-29-2004, 05:29 PM
Just above the pilot lite flame there is a copper tit connected to a copper wire that runs to the gas control. This is a manual control that will not less gas flow into the main control unless the pilot lite is on. When they go bad it send a message that your pilot lite is out. This is a very inexpensive item and you can change it in a matter of a few minutes. They are sold at most hardware and home centers. It is a good idea to always have a new one hanging near the furnace.
Hope that helps.

High C
02-29-2004, 05:41 PM
Some furnaces have safety switches that cut off the gas if the door or access panel is removed. Look for such a switch and try holding it in manually to see if that's the problem.

Keith Wilson
02-29-2004, 05:48 PM
Gerald is on the right track, IMO. Over the years I've has to replace bad thermocouples on various gas appliances four or five times, and any other part only once (electric ignitor in an oven). The point of the thermocouple is to allow the main gas valve to open only if the pilot light is lit. Otherwise, if the pilot flame went out, it would dump a bunch of unburned gas into your house, generally something to avoid. When it fails, it fails safe. meaning that is prevents the main gas valve from opening even when the pilot is lit. They're usually pretty cheap and easy to replace, and if it was mine I'd try that first.

[ 02-29-2004, 06:48 PM: Message edited by: Keith Wilson ]

02-29-2004, 06:01 PM
Thanks Keith. I guess I have been out of the country too long. Be darn if I could remember the words to explain what I was trying to say.
Go to this site to see what we are talking about.

02-29-2004, 07:52 PM
In my experience with these, and it's been in the dozens with real estate investments, Gerald and Keith are correct.

I call it/heard it called a 'thermal couple?'

Anyway, I always replace this myself ... then, if still a problem, I call the repair man.

The part is typically around 10 bucks ... takes five minutes to replace.

In at least HALF of my experience, this part replacement has done the trick ...

02-29-2004, 10:58 PM
Just to be on the safe side, you might want to check that your homeowner's policy covers repair attempts by unqualified repair people (i.e: the homeowner) in case the house goes *BOOM*. Topping off the personal insurance and your will might not be a bad idea either - just in case. Of course, you could just bite the bullet and call a qualified repair person ;)

Keith Wilson
03-01-2004, 09:28 AM
Oh good god, Meerkat, it's just a gas furnace, not a nuclear reactor! Almost anyone of moderate intelligence can replace a thermocouple (which has nothing to do with the gas piping BTW), and with only moderate common sense, one can easily avoid blowing up the house. :rolleyes: Software guys! :rolleyes:

03-01-2004, 11:33 AM
HAH - If Dave Berry had written it, you would have laughed. tongue.gif

03-01-2004, 11:42 AM
No luck with this thing...

I have replaced the thermocouple, as well as totally serviced the whole thing. I cleaned the burners, checked the Spuds, and cleaned all of the electrical contacts. At this point it looks like I'm calling a service person. Though I am going to see how much it will run me. I can purchase a new gas control valve for $56, and a new coil for $12, so if the repair man is going to charge me $75 bucks just to show up there is no point...

Thanks for the help,


(BTW Meer, this is really pretty simple stuff. There is more of a chance to blow up a boat than there is to blow up a furnace. Basically you need to keep the gas from leaking..."

03-01-2004, 12:04 PM
Ok, ok! ;)

FWIW, when I was a kid we had a furnace problem kind of similar to this. Turned out to be a cracked combustion chamber that caused a draft that somehow kept the furnace from lighting off, even though everything looked correct.

03-01-2004, 04:11 PM
It WILL cost at least 75 bucks to figure out what's wrong.

Hopefully, it's not the heat exchanger. IF so, it is cheaper, in the long run, to replace said furnace.


03-01-2004, 04:28 PM
Well Brad, you hit the nail on the head with the $75 number...all caused by my stupidity...

So there was only one thing wrong with the stove in the first place...my thermostat. It's an electronic one, and the batteries were low enough not to turn on the stove, but good enough for the display and everything to work.

By the time I thought to check the batteries I had already mucked around with the furnace, and turned off the gas to the stove. The valve that the furnace used is on when it's in a diagonal position, not a horizontal position like you would think...

So it turns out that there was enough gas to run the pilot light, but not enough for the full furnace to run...Yep, my own stupidity caused this one...

So total cost:
$5.00 new thermocouple...
$2.00 new batteries
$70.00 gas repair man to turn valve on.

Boy do I feel dumb right now. I'm usually smart enough to figure this stuff out...plus that $75.00 was boat money.


High C
03-01-2004, 04:42 PM
Nahh, you just learned a valuable lesson, at a reasonable cost. Sometimes watching a pro do his thing will save you $$$ down the road. Like the other day when I had a guy come out and fix the Adler Barbor refrigerator on the High C. I can't bear to admit what he charged me to install a new thermostat and add freon. :eek: But next time I know to buy a manifold gauge and do it myself. He made the mistake of telling me the target pressures. Heh heh.... ;)

03-01-2004, 04:49 PM
Well, if it's any consolation, I once participated in an exercise that cost about $12,000 (including lost customer work time, plane fares for additional techs and fedexing of replacement parts) that involved tearing down and replacing most of a mid-70's computer system, only to discover, after 3 days of round the clock feverish activity, that it was a faulty on/off switch. :D