Trane TUD1B080A9H31B Error Code Continuous OFF: Check Power
What Does Code Continuous OFF Mean?
The White-Rodgers 50A65 IFC lights its diagnostic LED whenever it has power. When the LED is completely off, the board is receiving no electricity at all, so the furnace cannot run and shows no other codes.
This is the opposite of a continuous-ON light, which means the board has power but has failed its internal self-check. A dark LED points outward to the power supply: the wall switch that serves the furnace, the circuit breaker, the blower-door interlock, or — less often — the furnace's own low-voltage transformer.
Most of the time the cause is simple and safe to check: someone switched off the service switch (it looks like an ordinary light switch near the furnace) or the breaker tripped. If restoring those does not bring the LED back, the problem moves inside the furnace to the transformer or wiring, which is a job for a technician.
What You'll Notice
- The control board LED is completely dark with no flashing of any kind.
- The furnace does nothing on a call for heat — no inducer, igniter, or blower.
- The service switch on or near the furnace may be in the off position.
- The furnace breaker in the electrical panel may be tripped to the middle or off position.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Tripped circuit breaker or blown fuse | Most common | ✓ DIY fix → |
| Furnace power switch turned off | Common | ✓ DIY fix → |
| Failed transformer or wiring issue | Uncommon | ✗ Call a pro → |
How to Fix It: Restore Power to the Furnace
What You'll Need
Steps
- Turn off electrical power at the breaker and shut off the gas supply valve Before inspecting anything, set the furnace circuit breaker to OFF and turn the gas shutoff valve perpendicular to the pipe. If you smell gas at any point, leave your home immediately and call your gas company from outside.
- Check the furnace service switch Find the switch on or near the furnace cabinet — it looks like a standard light switch, sometimes inside a small metal box — and make sure it is ON. It is easy to mistake for a room light switch and turn off by accident.
- Check the circuit breaker At your electrical panel, find the breaker labeled for the furnace. A tripped breaker sits in the middle or off position; push it fully to OFF, then firmly back to ON. If it trips again immediately, stop and call a technician — that indicates a short.
- Make sure the blower door is fully seated The blower-compartment door must be fully closed for the door interlock switch to pass power to the board. Confirm the panel is properly in place and latched.
- Restore gas and power, then observe the LED Turn the gas valve back on (parallel to the pipe) and set the breaker and service switch to ON. The control board LED should light and resume a slow standby flash.
When to Call a Professional
Contact a licensed HVAC technician if:
- The LED stays dark after confirming the service switch, blower door, and breaker are all on.
- The breaker trips again immediately each time you reset it.
- You find scorched wiring, a burnt smell, or signs of water near the furnace.
- There is power at the switch but the low-voltage transformer produces no output (a meter reading a technician performs).
Frequently Asked Questions
Why is my Trane furnace control board light off?
A dark LED means the board is getting no power. The usual causes are an off service switch, a tripped breaker, or an unseated blower door — all easy to check.
My furnace breaker keeps tripping — what does that mean?
A breaker that trips immediately on reset signals a short circuit or failed component. Do not keep resetting it; have a technician diagnose it.
Could a bad transformer cause the light to be off?
Yes. If the switch, door, and breaker are all fine but the board stays dark, a failed 24V transformer or a wiring fault is the likely cause and needs a professional.
Sources
✓ Verified against manufacturer service manual — March 2026