York TM9V080B12MP11 Error Code LED Steady Off: No Power / Blown Fuse
What Does Code LED Steady Off Mean?
When the LED on the York TM9V080B12MP11 control board is completely dark, the board is not receiving any electrical power. The furnace is entirely non-functional — no heating, no cooling, and no fan operation will occur.
Start with the simplest checks: make sure the furnace circuit breaker in your electrical panel has not tripped, and verify the furnace power switch (typically a standard light switch mounted near the furnace) is in the on position. If the breaker trips again immediately after being reset, stop and call a technician — repeated tripping indicates a short circuit.
If power supply checks are fine, the problem is inside the furnace. A blown fuse on the control board is a common culprit. These small glass or blade fuses protect the board from damage caused by shorts elsewhere in the system. A failed transformer or a completely failed control board are also possible. All of these internal issues require professional diagnosis and repair.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| No power to control board | Most common | ✗ Call a pro → |
| Blown fuse on control board | Common | ✗ Call a pro → |
| Failed control board | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- If the breaker is on and the furnace switch is on but the LED remains off — an internal fuse, transformer, or board failure needs professional attention
✓ Verified against manufacturer service manual — March 2026