• My Ducane MPGA100B4B furnace is shortcycling (2 minutes from fan on to fan off)
  • The thermostat's Heat Anticipator setting doesn't seem to matter for the on-time, maybe the offtime changes
  • The thermostat is of the round mechanical variety, not digital
  • The furnace's control board seems to be blinking healthy codes - steady blink when off, faster steady blink when on.
  • The air filter on the bottom left side of the unit doesn't seem too dirty.
  • If I turn the thermostat to below-temp for a few seconds and then back above temp, the furnace will turn on again immediately for its 2 minutes.
  • It's cold in here!

What might it be? What can I check?

  • It is coding with Flame Failure Lockout blink now, but sometimes it goes back to a healthy blink. The ignitor is out - there's 120v going to it when the relay kicks in, but it doesn't get hot. Jan 24, 2012 at 18:12

1 Answer 1


Have you checked the temperature inside the furnace? It is possible the pilot light went out.

Disclaimer: I don't hold any special knowledge about furnaces. They are dangerous if tampered with. Re-lighting pilot lights can blow your house up. I don't recommend anything.

  • It has an ignitor, not a pilot light, but yes, that is broken. Jan 24, 2012 at 18:10

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