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Michael D 10-28-2012 04:26 PM

Need help w/furnace that cuts out

I've got an eight-year-old electric ignition Aire-Flo furnace with a Honeywell valve. When the thermostat or power is reset, the unit will fire up normally--blower then burner--but the flame goes out after 1-3 minutes. It will attempt several short and long phases of restart, sometimes getting as far as the ignitor glowing (though not always). When it does get as far as the ignitor glowing, about half the time it clicks and lights. However, these subsequent ignitions always go out after 10-45 seconds. So it's only successfully lighting every 3-5 minutes and only staying lit for a couple minutes max.

I've already pulled and sanded the flame sensor (really didn't look dirty). since it sometimes burns for 2-3 minutes, if it's a sensor issue, it's not consistent. Same with the ignitor--though the cycle doesn't always get to the ignition stage, or does and shuts down before the gas is released, the ignitor should not be a factor in the flame going out once it's lit. Problem also occurs with the panel open, so I don't suspect any airflow issues. I'm pretty new to this, but the only other thing I can think of is some timing issue with the valve itself. Hopefully someone here can suggest otherwise.

Weather's been crazy here and we've been back and forth between heat and air the last couple weeks, dunno if that would cause anything to act up...Thanks.

biggles 10-28-2012 04:55 PM

is there an Induced Draft Motor (IDM) on that unit with a pressure switch

Michael D 10-28-2012 05:58 PM

If the switch is a round thing about the size of an oil cap mounted to the motor with two wires and rubber hoses leading to the gas valve, burner compartment and (what I suspect is a condenser drain) white plastic box, then yes...

ben's plumbing 10-28-2012 07:29 PM

still could be flame sensor just cause it don't look dirty don't mean its not bad..sometimes cleaning don't help it needs replaced..ben sr

Michael D 10-29-2012 09:06 AM

Could be...seems to burn for rather inconsistent lengths of time, though. Wouldn't a bad sensor kick it off pretty quickly? It is one of the cheaper fixes, but still $35-$45--can these be tested? I'd like to get a few more ideas before I start trial and error replacements.

Any suggestions on the pressure switch and/or condensation drain box (I'm assuming that's what the white plastic cigarette pack sized thing is in the electrical compartment--seems a poor placement)...might my problem be related to these?

Michael D 10-29-2012 04:33 PM

Just checked the hoses to the pressure switch, no clogs. Condensate trap draining fine, too. Not sure what next step is. Get a voltmeter and check the switch?

HVACTECH96 10-29-2012 06:36 PM

Make sure there are no dips in exhaust pipe that can collect water.If there is water collecting you will see the pin in center of pressure switch pulsate in and out while running.

Michael D 10-29-2012 08:05 PM

Pressure switch is closed black plastic circle--don't see any pin or movement. Looks like exhaust is all PVC--no dips or sags...

Had it running for 45-60 minutes about an hour ago (inducer tried to start for a second, quit, then came on and ran without interruption). House temp climbed three it's back to the same tricks.

Michael D 10-30-2012 11:28 PM

Still working on this...any other suggestions?

how 10-30-2012 11:40 PM

Is there a flashing led diagnostic light on your furnace board that might be visable through a door viewing port. If so, record the sequence of flashes and compare it to the diagnostic legend usually found inside on one of the furnace doors.

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