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Burners shut off before reaching desired temp


tcupps1
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Let me start by saying that the motor has been acting up for a couple of weeks. It stopped and just hummed a couple of times, the burners shut off before the desired temp is reached, but the fan conyinues to run, then after a couple of minutes the burners start back up, but only for a couple of minutes. Today I removed the motor and took it apart and the sleeve bearings, I thinks thats what they are?,they have sponge material wrapped around the sleave,I applied lubricating oil to the ports until the sponges were saturated, because they were dry, I put everything back together and it still does not seem to blow as well as it used to , maybe the motor is going bad and not reaching its high RPM and the system shuts the burners off? Is this possible or does anybody have any ideas? thanks tcupps1

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Terry,

Sure sounds like the motor is kaput!

Everything you report makes sense for the system to sense high temp and shut down before doing extensive damage. Re-lube the motor will likely get it going, but only for a limited time. Ain't good for furnace to shut down repeatedly on high temp limit.

The good news is that it sounds like everything else is functional.

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It sounds like it's short cycling for some reason. It's probably unrelated to the motor. It might be overheating due to a clogged filter or there might be something obstructing the flue or any one of a dozen other potential causes. If it's not too old a unit, it might be blinking a code at you telling you what ails it. Check the manual.

There's no way that we can diagnose it for you over the internet. Go down to the library and sign out a copy of Time/Life's Fix It Yourself Home Heating and Cooling and then work through the trouble-shooting guide in that. If you don't have the ability to, through the process of elimination, follow that guide and figure out on your own what's causing it to short cycle, it's probably not a good idea to dink around with it or you risk doing something that could poison you and your family with CO. You're better off calling a repairperson than gambling that someone here can help you sight unseen.

ONE TEAM - ONE FIGHT!!!

Mike

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Mike,

I am thinking the fan is not moving air across the exchanger and allowing limit to shut the burner down. Slow running fan would have same net effect, less air movement and greater heat accumulation, as a dirty filter or other restriction. Clogged flue likely would shut the whole thing down.

You are right that it could be a variety of things and Terry should call a tradesperson!

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well I took the motor down to get it tested and they said the bearings were shot,so I purchased a new motor and installed it, it seems to be working better BUT, It is still shutting the burners down before it reaches the desired temp of 70, gets to about 68 now, I don't know , are the burners suppost to shut off frequently on its way to the desired temp?, I thought they would stay on the whole time until it gets there. man, this is really frustrating,[:-banghea,I can't afford to have someone come in to look for the problem.I'm going to keep working on this ,but I do thank you all for your help.

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Hi,

What you are describing is short cycling. If you can't afford to have a tech look at it, do as I suggested - go to the library, get some references and then follow their trouble-shooting steps to diagnose short cycling. Frankly, we've done about all we can do for you; after all, this is a site for home inspectors, not HVAC techs. We usually run a system, note that it's short cycling and then recommend that the client have the system inspected and diagnosed by, guess who (?), an HVAC tech. We don't try and diagnose the issue or prescribe a fix 'cuz that's outside of what we do.

Good luck with that.

ONE TEAM - ONE FIGHT!!!

Mike

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Its about ten years old, but I also closed off the ducts in the upstairs at the beginning of winter to save on the heat bill, but maybe that is constricting to much and building the heat up and shutting it down to soon, so I opened the dampers to see if that would make a difference.

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