The furnace does not start at all; there are no lights on the Danfoss controller, and the blower and burner are inactive.

Safety first: Turn off the circuit breaker before opening electrical compartments. Use a non-contact voltage tester if available.

Steps:

• Check breaker and switch: Verify the furnace circuit breaker is in the ON position and the furnace service switch is also in the ON position.
• Inspect internal fuse: Many Danfoss controls have an internal low-voltage fuse. With the power off, remove and visually inspect the fuse. Replace only with a fuse of the same type and rating.
• Check door interlock: Ensure the blower door is properly installed to engage any door switch.
• Verify transformer output: A technician can measure the low-voltage transformer output to confirm it is supplying power to the control.