York YP9C three red flashes at low fire only: pressure switch, pressure sensor, or the vent

What Does Error 3 red flashes Mean?

Three red flashes reports the pressure switch open with inducer pressure above the switch setpoint, meaning the switch is open when it should be closed. The reason this shows up at low fire is written into the same manual. The switch is mounted on the draft inducer and proves flow at the start of each cycle. The manual then states that it may be open under certain conditions when the burners are lit, because the pressure sensor on the control board is the primary flow sensor. Minimum firing rate is where inducer speed and the pressure the switch sees are both lowest. Applies to: York Affinity YP9C modulating condensing furnaces and the TP9C, CP9C and LP9C models sharing the same installation manual This applies to the modulating YP9C family and the models sharing its installation manual, which use both a pressure switch on the inducer and a separate pressure sensor on the control board. Single and two-stage York furnaces without that pressure sensor read a pressure switch fault differently. Owner-safe checks: Watch a full cycle through the door view port and note how many seconds pass between ignition and the fault. | Retrieve the stored error codes with no thermostat call active, and write them down in the order they replay. | Check that the outdoor vent and combustion air terminals are clear of snow, leaves and nests from outside the building. | Confirm the condensate drain is running freely, since a separate condensate pressure switch can shut the burners off. Qualified technician: Testing the pressure switch, its hoses and the pressure sensor means working inside the burner compartment on an energised appliance, which is service work. | Any assessment of the vent system, combustion air piping or the inducer belongs to a qualified technician, and pressure switches must never be adjusted to allow operation.