Furnace will not stay on for very long

[clj2]

Hi, my gas heating system will not stay on, here is the problem

-hear a motor, then the gas coming on/burners lighting
-fan comes on, heat starts blowing out after a minute or so
-heat runs 5-6 minutes
-air coming out of vent gets cold, fan shuts off after about a minute
-after shutting off, I hear a humming noise like a motor
-I hear the burners light and the furnace come on again, fan comes back on, and about 30 seconds later it starts back blowing out hot air

then, after running around 5 minutes more, it shuts off for good. It used to come on and run however long it needed to, but suddenly started this one afternoon a couple of weeks ago. The heat is and always has been VERY warm, and this has been a very good unit. I have no idea on an age or even make, all there is on it is a warning sticker, but I would guess it's around 15 years old. This is my third winter in this house and I know really nothing about the history of the unit. The filter is clean and I don't know of any airflow that is blocked. I am calling someone out on Monday. There was some sort of board replaced in the blower/fan a couple of years ago that I understand was connected to the heat also, but I don't remember what it was called- this was in the summer when the fan wouldn't stay on. The unit works properly but just doesn't stay on long enough and has to fire back up immediately after. It can only heat for about 7-8 minutes at a time without doing the off/on thing. It has not been serviced recently...I know, that's not good, but I can't change the past...

Is there any hope for it? I hope I don't have to get a new unit, I can absolutely not afford one

I am just curious about what could be wrong. I have gone through everything I can possibly think to do without having to call someone out. I am thinking the limit switch might be dead or something? Trying not to sound so stupid so I know what all to say when the technician comes. Thanks.

[sweat hog]

You have good info on how the furnace is behaving, be available when the serviceman is there and tell your observations. It will help save some time in checking out the furnace. Getting it fixed will save money and give you peace of mind.

[Wheelbaron]

Please read the site rules, this is not a DIY forum. You could have a serious problem there. You need to call a qualified pro. I strongly suggest that you shut off the unit RIGHT NOW. If it is not what I am thinking it might be, then its not that big of a deal, and should not cost too much to repair. However, either way letting the unit short cycle like that will break other parts such as the inducer fan motor.

Don't think about how much it will cost to get it fixed, think of what it may cost if you don't get it fixed....

Good luck

[Roadhouse]

it sounds like a high (excessive heat) limit switch or possibly even a gas problem. Why needs to be determined so call a service company as this doesn't sound like you'll be needing an entire new unit.

[cboe]

when the service tech. arrives make sure he adjusts the heat anticipator

[Paradigm Rob]

I agree with Roadhouse: sounds like an issue with too much heat/not enough airflow.

May be a limit switch setting (if its adjustable) or duct sizing issue.

[beenthere]

If you haven't cleaned or replaced your air filter since this started. Do it now. If you still have the problem after that, then call for service.

[dandyme]

If you haven't cleaned or replaced your air filter since this started. Do it now. If you still have the problem after that, then call for service.

that was my thought, reading the title.

[clj2]

Filter was changed a week or so ago after it started, first thing I ever tried. The old one wasn't that dirty itself. Thanks for all of your help

[Air Movers]

I agree with Roadhouse: sounds like an issue with too much heat/not enough airflow.

May be a limit switch setting (if its adjustable) or duct sizing issue.

I agree its the limit switch but I hope she gets an hvac tech out there and not somebody from the gas company!!! I make alot of money going around and fixing things after the propane guys touch it, Is the furnace natural or LP

[Kevin O'Neill]

Filter was changed a week or so ago after it started, first thing I ever tried. The old one wasn't that dirty itself. Thanks for all of your help

If your filter is a pleat, replace it with a cheap fiberglass filter. If that does not help, call a tech.

[clj2]

I had been using a fiberglass filter that was not that old and was clean, but I replaced it anyway when this started. Didn't help.

The more I read on similar situations, it sounds like it's a limit switch issue. Should I tell the technician I think this may be it, or just let them look around for themself? I don't want to throw a wrong idea out but then again would like to throw an idea out if it may be helpful.

It's a natural gas furnace. I am calling a HVAC company. Thanks

[Roadhouse]

I had been using a fiberglass filter that was not that old and was clean, but I replaced it anyway when this started. Didn't help.

The more I read on similar situations, it sounds like it's a limit switch issue. Should I tell the technician I think this may be it, or just let them look around for themself? I don't want to throw a wrong idea out but then again would like to throw an idea out if it may be helpful.

It's a natural gas furnace. I am calling aN HVAC company. Thanks

Pet peeve of mine, sorry.

As already said simply just relay the info you have of the symptoms as that'll let the tech know, just like we kinda sorta knew as best we could over the net and not being in front of your furnace, what to look into to.

I'm sure he'll be able to tell you why the high limit switch is cutting off the furnace in the first place which is the problem, not the high limit tripping, that works.