York TM9V080B12MP11 Error Code Steady On (Any Color): Control Failure
What Does Code Steady On (Any Color) Mean?
A steady, non-blinking LED on the York TM9V080B12MP11 control board signals a control board failure. The LED should always display a flashing pattern during normal operation — slow green for standby, slow amber during heating, or numbered red flashes for faults. A solid, unchanging LED means the microprocessor has stopped executing its control program.
Try resetting the furnace by turning off the circuit breaker for 30 seconds and then restoring power. If the LED resumes its normal slow-flash pattern, the board may have experienced a temporary software fault. If the LED goes directly to a steady-on state after the reset, the board has failed permanently. The control board is not field-repairable and must be replaced.
A qualified HVAC technician must install the replacement board, ensuring it is the correct part for this model. After installation, the technician needs to verify all system functions including ignition sequencing, blower operation, and safety switch monitoring.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Failed control board | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- When the LED stays solid after a power reset — the control board needs professional replacement
✓ Verified against manufacturer service manual — March 2026