Goodman Furance cuts off intermittently

Goodman / GMC 125-5 gas furnace in an unconditioned crawl space with concrete floor surrounded by dirt. When the outside temp gets 40 degrees or less in Atlanta, GA, the heat stops. When I immediately try to restart it, the igniter glows orange for 7-8 seconds, but no gas flows.

We can turn off the thermostat wait 15-30 min and it fires back up. Sometimes it’ll work for only 15 mins. Sometimes it’ll work until it gets cold again a few weeks later. Could the outside temperature affect gas flow? or Does the furnace working overtime because of the low temps cause something to overheat? loosen? And shut the whole system down? What could explain the waiting a short time then working again?

Gas water heater 6 feet away has a standing pilot light that stays lit.

Four techs have been out here and tried various fixes that did not work. The following parts have been replaced: thermostat, capacitor, board, gas valve, vent fan unit. Flame sensor has been sanded.
Has anyone fixed the exact same problem?

 

The pattern you describe is of a long operation of the furnace during cold temperatures, with the BURNERS shutting off and not turning back on for a half hour or so. Does the fan that circulates air around the house continue to operate when the burners shut off?


This suggests that the limit switch is opening because the furnace is overheating. Use a multimeter to see if the limit switch is opening.

And to replicate the situation, turn the thermostat up to 80 or 90 to force the furnace to continue to run. See if that causes the burners to shut off as you describe and then check to see if the limit switch has opened, thereby shutting off the burners.

Unfortunately, I can't find a furnace manual with a circuit diagram for the model furnace you report.

 

You did not mention about the HSI being tested or replaced. It may be on its way out with a crack developing through it, where it works one time but not another. This has fooled people because they see the glow and thinks it should work. It not only has to glow....it has to REALLY glow.

You said it does not get gas. If the HSI is going out, usually it still will get gas. But some people say the wrong thing. They think it is not getting gas because they see the glow and presume no gas because it does not fire off. Do you hear or feel with your fingertips, the gas valve click within 30 seconds of the HSI first starting to glow? If you hear/feel that click, there is a good chance the gas valve is being energized to open. If you have natural gas with a meter, you should also see a 1/4 foot dial on your gas meter move some, in the time period after the HSI has glowed 30 seconds. If that dial has moved, you are getting gas.

 

with the ignitor only glowing for 7-8 seconds....you need to look ath the venting system.is it a 80 or 90...also look at air intake since this is in a crawl space......

 

We do not know how much the poster understands furnaces. When he says the ignitor gllows for 7-8 seconds, he may not be starting to count from the ignition control module click sending power to the ignitor. He might only have counted when he starts seeing the glow, at some stage of it. Poster needs to clarify for us.

IF the ignitor is only glowing for 7-8 seconds, that is not long enough, and may indicate either the HSI is faulty or the board, or something else in the circuitry shutting down. But he did say the board got replaced....but not the HSI.

I wonder what those techs made of the 7-8 second thing.

 

Hi Guys,

I've got the same exact problem as Ronster... My girlfriend's Goodman GMP 075-3 upright gas furnace stops igniting when the temperature in her garage dips south of nippy. We just had a guy come out and confirm what I figured out the night before: no gas is getting through the valve. I've done my fair share of working on cars, computers, washers, etc. so this is a new project for me...

What other parts are involved in actuating the gas valve that could possibly be the culprit? I've already confirmed (by holding a lighter up to the gas/air mix that there's no gas to be burned. The element glows 7-8 seconds periodically while the fan motor is going but no combustion is occurring. That much is obvious.

Thanks for any help.

 

Gnerally speaking, once the pressure switch closes, the ignition control module turns on the igniter for 20-30 seconds or so to get hot, then turns on 24 VAC to the electric gas valve, which should turn on the main burner gas and which should then light off the hot surface ignitor.

Since the HSI gets hot, the likely reasons for no gas flowing would be 1) gas turned off at the electric gas valve, manual shutoff valve or gas meter 2) defective ignition control failing to turn on the 24VAC to the electric gas valve 3) electric gas valve with a burned out coil or other defect.


So check the gas supply to the furnace first. Then use a multimeter to check to see if the 24VAC power is being turned on to the electric gas valve. If it is, you need a new electric gas valve. If it isn't, you need a new ignition control module.

 

Ok,

After getting a $435 quote earlier this afternoon, we thought it wouldn't hurt to ask my friend (a contractor who's painting the house today) to take a look at it.

After verifying 24 volts was going to the gas valve, he gave it a whack with the hammer and managed to get the valve to open up, and now we have heat again...for the time being.

I neither recommend this solution for everyone nor foresee this as a permanent fix, but it'll help relieve some stress on my girlfriend while she prepares for the big New Year's Eve bash tomorrow. We'll see how it holds up.

 

I would say your friend is well placed as a house painter.

 

But nonetheless - sounds like the sort of guy Martin would like to have with him if on a deserted island.

If the furnace had not been used a lot, the valve simply may have gotten sticky from sitting - and now may work just fine for the rest of the heating season. Have seen it. Also have whacked on gas valves and had then go, then work thereafter.