York YP9C twelve red flashes: the ID plug is not connected
What Does Error 12 red flashes Mean?
The manual assigns twelve red flashes to the ID plug not being present or not connected properly, and directs the check at a loose plug or loose wires in the plug. It is a connector fault, not a control board failure. Applies to: Affinity YP9C modulating gas furnaces This flash code is published in the York installation manual for the Affinity YP9C modulating gas furnaces. Other York furnace families use different control boards with different flash tables, and a twelve-flash code on another manufacturer's furnace means something unrelated. Owner-safe checks: Watch at least two complete flash groups and note both the colour and the count before recording it. | Record whether any work was done inside the furnace before the code appeared, and by whom. | Check that the furnace has power and that no breaker has tripped, without opening the cabinet. Qualified technician: The ID plug and the control board sit inside a cabinet containing gas piping and line voltage connections, so reseating or replacing the plug is technician work. | The manual warns against bypassing any safety control or adjusting a pressure switch to allow the furnace to run.
Diagnostic Tree & Resolution Protocol
Official manufacturer root cause analysis and step-by-step diagnostic workflow.