Furnace will not start, controller display shows E0 and burner never attempts to ignite

Safety first: Turn off power to the furnace at the service switch or breaker before opening any panels. Do not bypass safety devices.

Steps:

• Verify thermostat demand: Set the room thermostat to a temperature higher than room temperature and ensure it is set to HEAT mode.
• Check thermostat wiring: At the Danfoss furnace control module, locate the thermostat terminals (often marked RT/RT or TA/TB). With power off, inspect for loose or broken wires. Tighten terminal screws and repair any damaged cable.
• Test thermostat circuit: With power off, temporarily jumper the thermostat terminals at the controller (consult the Danfoss wiring diagram on the furnace door). Restore power and see if the E0 clears and the burner starts. If it does, the thermostat or its cable is faulty.
• Check external enable contacts: Some Danfoss furnace controls have an external enable or safety loop input. Confirm any external limit, pressure, or interlock contacts wired in series are closed and not tripped.
• Reset controller: After correcting wiring or thermostat issues, power-cycle the furnace and clear the error according to the Danfoss control manual (often by pressing and holding the reset key).

If the controller still shows E0 with a confirmed call for heat, the control board input circuit may be defective and should be evaluated by a qualified technician.