Tappan Furnace won't stay on for more than a minute...cycling


Old 11-21-08, 06:49 PM
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Tappan Furnace won't stay on for more than a minute...cycling

1. I live in Michigan. Current ambient temp 20F 2. 2 story house, 2x4 frame, insulated, aluminum sided 3. 4 year old Tappan FG6RC 100C-16B 4. Nat. Gas 6. Thermostat is a 5 yr old Honeywell. 7. Thermostat clicks on. Induced draft fan runs for ~30 sec. Gas valve clicks open, flames light, good fire for ~10-15 seconds. Then the blower starts & gas valve immediately closes. Blower runs, moderately cool air for ~1 min, then blower shuts down and immediately induced draft fan restarts. Cycle repeats. Perhaps after 4-8 cycles, the furnace will finally stay on and keep the burners lit WITH blower running and heat the home. Occasionally (maybe 1x a week), gas valve opens, then closes after 2 sec, presumably due to failure to ignite (haven't watched). The thermostat is NOT clicking off - it wants the furnace lit the whole time. Have tried using a wire brush to clean off the flame detector. It was not that dirty. No blinking lights inside furnace during cycling - just a steady red light all the time, and a steady greenish-yellow light when flames are lit. Thanks for help!
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Old 11-22-08, 11:53 AM
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Does it shut off like this when the stats is just left alone for it's normal call for heat, or does it also shut down if you turn the stat way up for testing?

Digital stat?

I always like to actually test the thermostat terminals in the furnace, to make sure the stat is not shutting off. If the stat shuts off, the 24vac power gets killed between the W terminal and ground.

I'd volt meter test at pressure switch, and also incoming power to control board or module, to see if it loses power on the 24vac circuit. If pressure switch loses current, you might have something like condensate water backed up from the drain line and needs blowing out both ways.

I'd make sure all your plug in connections are good, that are at all the safety switches and on the board or module.

Depending on type of blower fan turn-on mechanism, it is possible house is too cold to keep fan switch activated, until house warms up some. Although I'd think the blower would just shut off, and not the flame and inducer also.

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