York furnace: Johnson Controls (System Lockout)


Old 12-05-18, 10:29 AM
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York furnace: Johnson Controls (System Lockout)

I have a York P2DPD12N natural gas furnace that just experienced a system lockout, one flash of the diagnostic LED. It happened during the morning warm-up after a cold night. The control board is a Johnson Controls G951ADB-1403.

Is there any method to put the control board into diagnostic mode to learn exactly what is locking out the system?
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Old 12-05-18, 06:07 PM
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Welcome to the forums.

Has your furnace been routinely cleaned and inspected ?
A dirty flame sensor can cause this problem as well as a dirty filter.

The control stores up to five separate error codes. If more than five error codes have occurred since the last reset, only the five most recent will be retained. The furnace control board has a button, labeled "LAST ERROR" that is used to retrieve error codes. This function will only work if there are no active thermostat signals. So any call for heating, cooling or continuous fan must be terminated before attempting to retrieve error codes.

To retrieve the error codes, push the LAST ERROR button. The LED on the control will then flash the error codes that are in memory, starting with the most recent. There will be a two-second pause between each flash code. After the error codes have all been displayed, the LED will resume the normal slow green flash after a five second pause. To repeat the series of error codes, push the button again. If there are no error codes in memory, the LED will flash two green flashes.

To clear the memory, push the LAST ERROR button and hold it for more than five seconds. The LED will flash three green flashes when the memory has been cleared, then will resume the normal slow green flash after a five-second pause.
Old 12-14-18, 01:24 PM
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The LED flashes and the 2 sec pause are as you describe when there is an error that causes the furnace to shut-off.

But if an error occurs and a restart happens within the necessary time, the LED doesn't flash. For example, if the Hi-limit switch opens, the furnace will try to restart in 60 seconds, if this is successful the LED remains off. If not, then you get 4 flashes (IIRC).

I don't see a LAST ERROR button anywhere on this control board. There is no green LED, only a red LED next to the bundle as it enters the combustion area. Here are some of the control board, could you describe where I might find that button?


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