burners on armstrong furnace go out

amn8March 26, 2013

The burners on an Armstrong forced air furnace (model no. EG6G150DC20-4) will intermittently cut out. Once they go out completely, the pilot light remains lit and the fan continues to run until I shut off the furnace at the switch on the unit. I've replaced the flame sensor and have called two HVAC companies, one that replaced the control board and the other the gas valve - both to no avail.

Sometimes the furnace will run through and complete the cycle. When the burners do prematurely quit, I can usually get them running again by turning off and on the gas valve and the electronic ignition ignites the pilot, which in turn will light the burners. Sometimes I have to repeat this multiple times to get through the cycle.

Any ideas?

Thanks.

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Tinmantu

Did any check the temp across to see if it's dropping out on high limit. Do they witness the failure and begin checking the limit to see if it's open?

    Bookmark   March 26, 2013 at 11:25PM
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amn8

Unfortunately, they haven't witnessed the problem because it hasn't happened when they are here. Both speculated it could be the high limit. They questioned, though, if it was the culprit why the burners would kick back on immediately after either blowing out the pilot light or turning the gas valve off and back on -- which then triggers the electronic ignition that reignites the pilot and then the burners.

Are they right?

Thanks for the insight.

    Bookmark   March 26, 2013 at 11:50PM
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amn8

Third technician from another company speculated the ignition module is failing and could be replaced for $500. Here's his notes:

- Checked all wiring and connections
- Checked evaporator coil
- Cycled heat on and ran normally for 15 min
- Then the gas valve, which has been replaced, began to click internally
- Low voltage dropped to 16.2 a few times
- Pilot part did have 21.6 volts
- It did stop main burners momentarily while the pilot stayed on
- Blower is on high speed for heat

    Bookmark   April 2, 2013 at 10:03PM
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snoringcow

If there is one ...... Pressure switch.

    Bookmark   April 2, 2013 at 11:59PM
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amn8

I was told a bad pressure switch would cause the pilot to shut off. In my furnace's case, when the burners shut down, the pilot remains on, along with inducer. When it happens, it's my understanding that the voltage from the ignition module to the gas valve drops enough that it doesn't have enough juice to keep the valve open.

    Bookmark   April 3, 2013 at 12:24PM
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