I have a York Diamond 80 furnace Model# P4HUAR12N03201A. New construction 05 installation. Went away from this house for 2 months. Came back and furnace won't operate. System ignites, heats up plenum, blower comes on, and then the fire immediately goes out. Has a component failed or has the 2 month downtime created a different issue?

Look for a diagnostic LED through a clear plug in one of the front panels. Is it flashing? Observe the pattern/number of flashes and compare to service label - usually found on one of the panels or on the furnace control board. Post results.

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Originally Posted by KC13

Look for a diagnostic LED through a clear plug in one of the front panels. Is it flashing? Observe the pattern/number of flashes and compare to service label - usually found on one of the panels or on the furnace control board. Post results.

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No flashing.

I should have mentioned, check with furnace running. If short-cycle repeats but no LED code is displayed, the thermostat may be the problem. Bypassing the R-W circuit will allow you to check this.

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Originally Posted by KC13

Look for a diagnostic LED through a clear plug in one of the front panels. Is it flashing? Observe the pattern/number of flashes and compare to service label - usually found on one of the panels or on the furnace control board. Post results.

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No flashing.

Did the system function normally before you left? Was it idle the entire 2 months?

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Originally Posted by KC13

I should have mentioned, check with furnace running. If short-cycle repeats but no LED code is displayed, the thermostat may be the problem. Bypassing the R-W circuit will allow you to check this.

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Thank you very much. The furnace is running with a jumper on the R-W circuit in place. Although the furnace does not run continuously. It runs for a few minutes and then shuts down for a few minutes and then restarts again.

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Originally Posted by MarkwithaK

Did the system function normally before you left? Was it idle the entire 2 months?

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Yes. AC worked. Heat has not been used since last March or April and then it worked fine.

If you jumped R-W and you are still getting the short cycling then your stat isn't the problem. What condition is your filter in? You could be bouncing off the high limit switch.

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Originally Posted by MarkwithaK

If you jumped R-W and you are still getting the short cycling then your stat isn't the problem. What condition is your filter in? You could be bouncing off of the high limit switch.

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Filter is new.

Still no LED flashing?

I'm still leaning towards the high limit. Hard to pin it down without actually being there. The coil could be plugged. I would be interested to know what the temperature rise is.

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Originally Posted by S Jacobsen

Filter is new.

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FYI Solution found: Burner forced draft system had small particles of debris. Upon furnace restart one small particle partially plugged vacuum hose leading to the safety switch. Blowing out the debris allowed air draft hose connected to the switch to clear and the switch began to function again.