York furnace Steady off: No power to the board, or control failure
A dark LED means no power to the board or a control failure. On the related W/R boards York notes that a blown on-board fuse can still allow fault codes, which is a useful distinction.
Applies to: York, Luxaire and Coleman gas furnaces using the UTEC integrated furnace control boards documented in technical service letter ST-045-09. On the last generation W/R Emerson boards, York notes fault codes are possible with a blown on-board fuse.
What it means
The LED is powered by the board, so a dark LED means the board is not running. Before assuming failure, it is worth knowing how many ways a furnace legitimately removes its own power — the blower door switch cuts 115 volts whenever the panel is off, which means taking the panel off to look at the LED is what extinguishes it. York's documentation for the related W/R boards adds a helpful nuance: fault codes are possible with a blown on-board fuse, meaning a board can be partly alive with its fuse gone.
Most common causes
- The blower compartment door off or not seated, opening the door switch.
- The furnace service switch turned off — it looks like an ordinary light switch.
- The circuit breaker for the furnace tripped or switched off.
- A blown on-board fuse, usually caused by a short in the low voltage wiring.
- A failed transformer, so there is no 24 volt supply.
- A genuinely failed control board.
- A fault in the 115 volt supply to the furnace.
How to diagnose it
- Check the service switch near the furnace first. It is the most common answer and takes a second.
- Check the breaker panel for a tripped furnace breaker.
- Understand the door switch before concluding anything — removing the panel to read the LED is what turns it off.
- Note whether the thermostat display is blank, which points at the low voltage side.
- Note whether the breaker trips again immediately after being reset, which is a fault rather than an inconvenience.
How to fix it
- Turn the service switch back on, or reset the breaker, if either was off.
- Refit the blower door properly. A door not seated holds the switch open and the furnace will not run.
- If the breaker trips again immediately, stop and call a technician.
- A blown on-board fuse, a failed transformer, or a failed board is technician work. A blown fuse in particular means a short somewhere, and replacing it without finding the short blows the next one.
- If the furnace has been wet, do not power it up.
Notes
The door switch catches nearly everyone at least once. If your furnace has a sight glass, read the LED with everything closed rather than opening the cabinet to look.
Related
All codes for this manufacturer
York, Luxaire and Coleman furnace flash codes — every code, with what differs between models.