Furnace turns off prematurely

I have a Fridgidaire 90+AFUE furnace that, at times, will start and stop prematurely. By this I mean that I hear the pilot light start, then the gas turns on and starts burning, but then the gas shuts off after 8 or 9 seconds, then finally the blower motor turns on for about 30-45 seconds. This occurs over and over but I have yet to determine for how long. At first I thought my thermostat was failing (LUX brand) so I replaced it with a Honeywell - same thing. Is this normal behavior for a three year old furnace (this being the first winter that I've noticed the "problem")? I will admit to having done no real maintenance on this unit since I moved in so if it's a dirty/bad sensor or something else that's failing then I have nobody to blame but myself. If its not normal behavior what things can I try to resolve the problem?
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I'd try calling a heating contractor. If you don't know a good one, ask a few neighbors or friends.
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first thing. have you checked your air filter? i had a electronic air cleaner that would cause the same exact thing when it got too dirty.

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Sounds like a limit switch needs adjustment; have a yearly service done on it.
:I have a Fridgidaire 90+AFUE furnace that, at times, will start and : stop prematurely. By this I mean that I hear the pilot light start, : then the gas turns on and starts burning, but then the gas shuts off : after 8 or 9 seconds, then finally the blower motor turns on for about : 30-45 seconds. This occurs over and over but I have yet to determine : for how long. At first I thought my thermostat was failing (LUX brand) : so I replaced it with a Honeywell - same thing. Is this normal : behavior for a three year old furnace (this being the first winter that : I've noticed the "problem")? I will admit to having done no real : maintenance on this unit since I moved in so if it's a dirty/bad : sensor or something else that's failing then I have nobody to blame : but myself. If its not normal behavior what things can I try to : resolve the problem? :
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There's a sensor that either needs repair or replacing. For a skilled technician, it shouldn't take very long. Call a local HVAC contractor. Tell them you would also like a heater checkup.

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Thanks all for the input. I'm assuming you're referring to the heat/flame sensor - is this correct? If so, is anyone familiar with this Frigidaire model and the location of the sensor? I've read elsewhere that using a small steel brush to clean it might do the trick. Is this something that you would recommend doing on a monthly/yearly/seasonal basis?
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Clean it every evening. If that doesnt work, replace the furnace. Bubba
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look up your make and model and find the manual online at the manufacturer's website. search for spark ignitor or glow ignitor at www.grainger.com to see what they look like. gas furnaces for beginners require a checkup every two years [oil ones get an annual checkup].
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wrote:

Every two years??? Where did you make up that one, "buff" ? Bubba
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A hot surface ignitor should not be cleaned, you will crack it, then you will need a new one. If it is spark ignited, well I never found a need to clean those either. Sounds like low air flow caused by: 1) Restrictive air filter. 2) Restrictive or undersized duct system. 3) Registers turned of in parts of your house you are not using. 4) Blower speed set too low.
Other possibilities: Limit switch improperly set, heat anticipator on thermostat improperly set.
Stretch
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Here's a weird reason. I have a Goodman HE unit. It was behaving in an odd way, too. Making its initial startup noises, then stopping without actually going to the preheat step. I'd just moved into the house, so I stood in the cellar listening to the noises so I could describe them to the heating guy when I called. Standing right under the PVC vent pipe, I heard water gurgling. Whoever installed the furnace did a lousy job of installing the pipe hangers, so the vent was bowed downward almost an inch in the middle of its run to the outside, so water was collecting there. I propped it up, the water drained out, and the next time the heater started, it ran correctly. I still had my contractor come over to check the machine over. He said this heater checks for proper venting before turning on the gas, and that there must've been enough water in the pipe to cause a problem.
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That's not an uncommon problem, especially in housing developments.

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