York Error Codes & Diagnostics
Complete diagnostic directory for official York fault codes. Verify root causes, safe troubleshooting steps, and replacement part numbers before calling a technician.
York YP9C twelve red flashes: the ID plug is not connected
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.
York YP9C two red flashes: the draft proving circuit did not behave
Two red flashes on a York YP9C control points at the draft proving circuit: the pressure switch has not reached the state the control expects for the stage of the sequence it is in. The count identifies the circuit, not the component, so the inducer, the vent path, the condensate arrangement, and the switch itself are all inside the reading. Applies to: York YP9C modulating condensing gas furnaces documented in the York installation manual This applies to the York YP9C modulating condensing furnace as documented in its installation manual. York uses different flash tables on other furnace lines, and a modulating furnace proves draft across more than one firing rate, which changes what a fault at a particular stage implies compared with a single-stage appliance. Owner-safe checks: Count the flashes carefully through the sight glass, keeping the blower door closed so control power is not interrupted. | Check the outdoor vent and intake terminations from ground level for snow, ice, nests, or plant growth without climbing or probing. | Note whether ignition is ever attempted and whether the fault is linked to a change in firing rate. Qualified technician: Measuring draft pressure, testing the inducer, clearing condensate traps, and verifying switch operation at each firing rate are licensed gas-furnace tasks. | Any indoor smell of combustion products, or a carbon monoxide alarm, means leaving the appliance off, getting fresh air into the space, and calling the gas emergency number before anything else.
York YP9C three red flashes at low fire only: pressure switch, pressure sensor, or the vent
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.
York YP9C four red flashes: limit, sensor, or fuse
On the documented York YP9C control, four red flashes can mean an open high-limit switch, a defective temperature sensor, or an open 24-volt fuse. Confirm that the LED is red, not amber, before using that definition. Four amber flashes describes reduced heating capacity from restricted circulating airflow. Applies to: York YP9C, TP9C, CP9C, and LP9C furnaces covered by the cited manual This page covers the YP9C family and the TP9C, CP9C, and LP9C models named in the same York manual. The color is part of the code, and other York controls may assign a different meaning to four flashes. Owner-safe checks: Record the flash color and count through two complete groups without removing a furnace door. | With heating off, inspect the homeowner-access filter and confirm ordinary return and supply grilles are clear. | Note whether the thermostat display remains powered and whether the blower continues after the burners stop. Qualified technician: Fuse diagnosis, sensor testing, temperature-rise measurement, blower assessment, and safety-circuit work belong to qualified gas-furnace service. | Never bypass a limit or install a larger fuse. Either action removes the protection York intended the control to enforce.
York YP9C five red flashes: flame where the control did not ask for it
Five red flashes on a York YP9C control reports flame present at a time the control did not command it. That is a statement about the gas train rather than about ignition performance, so the furnace should be taken out of use and handed to a licensed engineer rather than reset and observed. Applies to: York YP9C modulating condensing gas furnaces documented in the York installation manual The flash table referenced here is the one published for the York YP9C modulating condensing furnace. York assigns flash counts differently across its furnace lines, and equipment from related brands on similar control platforms carries its own table, so the model on the rating plate governs. Owner-safe checks: Check for any smell of gas first, and if one is present leave the property and call the gas emergency number from outside before anything else. | Isolate the appliance using the service switch fitted beside it, which ends the cycling without touching anything inside the cabinet. | Write down whether continued warmth or burner activity was observed, and at what point in the cycle the flashes appear. Qualified technician: Gas valve testing, burner inspection, and flame sensing circuit measurement on a modulating condensing furnace are licensed gas engineering tasks. | Do not restore the furnace to service to see whether the code returns. A repeat cycle is the risk this code is warning about.
York Affinity YP9C seven red flashes: ignition lockout
On the documented York Affinity YP9C, seven red flashes indicate lockout because ignition did not succeed after three attempts. The control waits one hour before another automatic attempt. The pattern reports the outcome, not whether the cause is gas supply, ignition, burner, flame sensing, grounding, venting, or control. Applies to: Affinity YP9C modulating gas furnaces This flash count is scoped to the YP9C manual cited here. York LX, Latitude, rooftop, heat-pump, and newer communicating controls can use other code systems, so the model and LED colour must match. Owner-safe checks: With panels closed, save the seven-red-flash pattern and observe one startup only through the factory viewing area without forcing another attempt. Qualified technician: Venting, pressure safeguards, ignition, gas, burners, flame current, grounding, combustion, and control testing require licensed York service.