Furnace fails to operate, control LED shows no signal

What is going on

Dead board. No LED, no display, furnace does nothing. Start at power, work toward the control. Most of the time it is a tripped breaker, a door switch or a blown fuse before it is the board. Board swap is last.

Likely causes

• No 115 V power to the furnace or no 24 V power to the control module
• Blown fuse or tripped circuit breaker
• Open blower door switch cutting power
• Failed transformer
• Integrated control module is not working

Check in this order

1. Check 115 V power to the furnace and to the control module with a meter
2. Check the blower door switch is pressed in and making
3. Check for shorts in the 115 V circuit and repair as needed. A short will keep tripping the breaker
4. Measure 24 V at the control. If 115 V goes in the transformer but no 24 V comes out, the transformer is bad
5. Turn power off before any repair
6. Read the electrostatic discharge precautions in the manual before handling the control
7. Replace a non-working control module with the correct part

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)