Gas furnace woes

[GenesisGuy70]

Hi all,

Got a question about my gas furnace. It's a really old GE (I rent, or I'd replace it). So when the thermostat calls for heat the gas will ignite, heat the exchanger up, blower kicks on and then goes for maybe 10-20 secs. Then the gas shuts off, blower continues to run and then after maybe 60 secs the gas will reignite, it'll burn for maybe a minute then shut back off, blower continues to run and repeat. It does this every time the thermostat calls for heat.

Ideas? I looked for a flame sensor but I don't think this old thing has one. Not sure what to check for next.

Thanks

Throw

**Yes I know, I rent, so why not call the landlord. I will if I need to but if it might be something simple than I'd prefer to do it myself rather than have strange maintenance men in my house while I more than likely won't be home. Plus, I like learning these things.

 

[JayhawkRoy]

As a renter, I would not mess with a gas furnace I don't own. Contact your landlord and let him come diagnose or send a repairman to diagnose.

What you describe is a potential safety issue, and should be dealt with soon.

Someone in my family was always able to take off from work, so the serviceman was not alone in the house. If you are interested, you are also learning from someone who has a better chance of knowing what he is doing.

 

[MNgopher]

Call the landlord. Nice sentiment to fix it yourself, but it isn't yours to mess with.

When I rented a house, the repairman called me directly to setup the time to be there after being contacted by the landlord, and the bill went to the landlord.

If you want to learn, learn from the repairman when he's there.

 

[toneydoc]

Those responses are good advice. If you screw something up, you are likely liable.

And I really hope you do not cause a fire and burn down the place. That will likely cost you a pretty penny or maybe even more if life is involved.

Let the professional licensed and insured guys do this, Please!

 

[Tdbo]

Originally Posted By: MNgopher
Call the landlord. Nice sentiment to fix it yourself, but it isn't yours to mess with.

When I rented a house, the repairman called me directly to setup the time to be there after being contacted by the landlord, and the bill went to the landlord.

If you want to learn, learn from the repairman when he's there.



This

 

[Wolf359]

It's not simple. As a landlord, I'd rather you call in a professional. I've seen many renters make things worse by trying to fix things themselves. And how much insurance do you have if you blow the place up or if everyone gets killed/sick from carbon monoxide poisoning?

 

[Johnny2Bad]

It's probably the thermocouple, which is cheap, and fails often enough to be considered a wear item.

It needs to be heated and controls gas flow; when working properly it just works, when not working properly you will experience what you are experiencing.

Since you're not a homeowner this is really not your problem, so you should have the landlord take care of it. And as someone who for a time rented a house out, I want you to call me and I want to pay for it, because knowing the condition of the property is important to me. As an expense, I'd save about 22% of the total cost via tax deduction, but money isn't the issue.

See:
http://heightslibrary.org/materials/hrrc/29-Heating-Cooling/THERMOCOUPLE_REPLACEMENT.pdf

But I've added the above in case someone reads this, owns the furnace, and wants to spend $10 instead of $110.

 

[NMBurb02]

Sounds like the fan/limit switch is killing the burners because of an overheat situation. This video explains what the switch does:



So the switch activates the fan but the temp in the heat exchanger keeps climbing (it generally stabilizes as the fan moves air through the exchangers), hits the high limit, and kills the burners.

That is my guess, anyway. Call in a pro.

 

[Bluestream]

Sounds like a plugged AC coil or plugged filters...your overheating safety switch is kicking in

 

[Bluestream]

Could be a broken fan belt if your unit has one

 

[JimPghPA]

Originally Posted By: Bluestream
Sounds like a plugged AC coil or plugged filters...your overheating safety switch is kicking in


+1. When was the last time the furnace air filter was changed? If the air filter is clogged there will be too little air flow through the heat exchanger and the heat exchanger temperature limit switch will trip and shut off the gas.

 

[CKN]

I had that problem once. Two birds got in to the exhaust pipe in the roof. They died of course, and they caused back pressure, causing the furnace to go in a safety mode and cut off.

 

[silveravant]

Not the thermocouple. If the pilot is on the thermocouple is ok.

Take off the cover of the fan control and observe the dial when the furnace is operating. See the video above. If it is hitting the high limit there may be some kind of obstruction in the air flow. How does the filter look?

 

[skyactiv]

If it's a thermocouple or your furnace has one, I hope your rent is cheap.

 

[Kuato]

Had a similar issue in a rental once. (agree with calling the landlord) Turned out the cooling fan was missing 1 blade out of 8, and the resulting vibration was causing a fan overheat. Took 3 different techs to come out and check it, they finally sent the old guy, "the fixer" whose experience showed when he went right to the cause.

 

[JimPghPA]

If it is a clogged air filter, you could temporarily run it with the air filter removed. If it does not short cycle with the air cleaner removed then you have proved that the air cleaner is causing too much restriction of flow.

 

[GenesisGuy70]

I'm fairly certain the fan limit switch is the culprit. I've adjusted it to where the fan comes on at a very low 70 degrees and it still allows the plenum to reach the 200 degree limit. When I first looked at it, it was set to come on at about 130 and like I said I've got it as low as it will go and it still trips it at 200. Not an airflow issue either. I've got good air flow coming out of all vents and the supply is 100% clear. Even took out the air filter and that made no difference. I can't set the 200 limit any higher. There is a manufacture installed like rivet thing that prohibits it.

I have noticed that when the thermostat first calls for heat and the burners come on the switch dial rotates veryyyy slow and then once it actually kicks on the fans it spins much much faster....all the way to 200 and then shuts the burners down.

Faulty limit switch? It isn't that old. It's much newer than the furnace itself. Looks like it was just replaced not that long ago.

 

[GenesisGuy70]

Follow-up:

Called in the pros. Definitely a problem somewhere. He said either the limit switch is faulty or the ducts in the sealing have collapsed and are impeding air flow. He said it's been a common problem is these old buildings because they're not metal, he said they're like a fiber compound something or other. Whoever thought of that originally wasn't the brightest. They didn't think long term. I'm trying to talk him into just replacing everything and I think I've almost got him sold on the idea. Crossing my fingers!