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Error code reference

York Furnace Error Code LED on constantly

The control discovered an internal fault during its self-check procedure; all operations cease.

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The control discovered an internal fault during its self-check procedure; all operations cease.

First step from the service manual

Check for voltage spikes or supply voltage too high or low. Reset the control by breaking line voltage for 30 seconds. If issue persists, replace control.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What LED on constantly means on a York furnace

A constantly illuminated LED on a York furnace control board indicates that the control module has detected an internal fault during its self-check routine. This self-check is a diagnostic procedure the control runs to verify the integrity of its own circuitry and logic before allowing normal furnace operation to proceed. When this check fails, the control immediately halts all operations, including ignition, blower activation, and burner sequencing, to prevent potentially unsafe or erratic behavior.

The internal fault condition is most commonly triggered by abnormal supply voltage conditions. Voltage that is too high or too low, or transient spikes caused by utility disturbances or nearby electrical equipment, can corrupt the control board's operating state and cause the self-check to fail. Because the board is monitoring its own internal logic, a failed self-check cannot always be attributed to a single external sensor or component. The board itself may have sustained damage from a voltage event.

The recommended initial response is to break line voltage to the furnace for a full 30 seconds, then restore power to allow the control to re-run its self-check from a clean state. If the LED remains on constantly after this reset, the control board has an unrecoverable internal fault and requires replacement. Persistent failures that return immediately after reset often point to either chronic power quality issues at the installation site or a control board that has been permanently damaged.

Source: manufacturer service documentation.

Common causes of LED on constantly

  1. 01

    Voltage spike or power surge

    Wiring / connection

    A sudden surge from the utility supply or nearby electrical equipment can corrupt the control board's internal state and trigger a self-check failure. Check the supply voltage at the furnace disconnect and look for signs of prior surge events such as discoloration or burnt smell on the board.

  2. 02

    Supply voltage out of acceptable range

    Wiring / connection

    Voltage that is consistently too high or too low prevents the control from passing its internal self-check. Measure the line voltage at the furnace to confirm it falls within the required operating range before replacing any components.

  3. 03

    Control board internal failure

    Part replacement

    If resetting line voltage for 30 seconds does not clear the constant LED condition, the control board itself has an unrecoverable internal fault. Replacement of the control board is required.

  4. 04

    Intermittent or poor line voltage connection

    Wiring / connection

    Loose wiring at the disconnect, breaker, or furnace terminal block can cause fluctuating voltage that triggers repeated self-check failures. Inspect all line voltage connections for tightness and signs of arcing or corrosion.

See the test procedure for each cause

Frequently asked questions about LED on constantly

What does LED on constantly mean on a York furnace?
A constantly illuminated LED on a York furnace means the control board detected an internal fault during its own self-check procedure. When this fault is found, the control immediately stops all furnace operations, including heating and blower functions. The furnace will remain shut down until the fault is resolved through a reset or board replacement.
Will resetting the furnace clear the constant LED condition?
A reset can clear the fault if the root cause was a temporary voltage spike or transient power disturbance. To reset the control, disconnect line voltage to the furnace for a full 30 seconds, then restore power. If the LED comes back on constantly after the reset, the control board has a permanent internal failure and must be replaced.
How do I fix a York furnace that shows a constant LED fault?
Start by checking the supply voltage at the furnace disconnect to confirm it is within the correct operating range and look for evidence of power surges. Then break line voltage to the unit for 30 seconds and restore power to allow the board to re-run its self-check. If the constant LED condition returns immediately, the control board will need to be replaced by a qualified technician.
Is it safe to run my York furnace when the LED is on constantly?
No, the furnace has already shut itself down completely as a result of this fault. The control board intentionally halts all operations when it detects an internal fault, so the furnace will not ignite or run in this state. You should not attempt to bypass or override the board, and the fault should be diagnosed and corrected before returning the furnace to service.
How much does it cost to fix a constant LED fault on a York furnace?
If only a reset is needed, there is no parts cost, though a service call to diagnose the voltage conditions may run in the range of $75 to $150 depending on your area. If the control board requires replacement, parts and labor combined typically range from $300 to $650, depending on the specific board and local labor rates. Addressing underlying power quality issues such as installing a surge protector may add additional cost but can prevent repeat failures.

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