Display shows C7, furnace will not start, fan does not run

Safety first: Isolate the appliance from mains and gas. Wait for internal components to cool.

• 1. Check fuses: Locate the internal fuses on the Junkers control board. Inspect and test with a multimeter. Replace only with identical rated fuses if blown, and investigate cause.
• 2. Inspect fan wiring: Ensure the fan plug is fully inserted into the PCB socket. Look for burnt pins or melted plastic. Repair or replace as needed.
• 3. Fan resistance test: Disconnect the fan and measure motor winding resistance according to Junkers specifications. An open circuit or short indicates a failed fan motor that must be replaced.
• 4. Power to fan: With the furnace calling for heat and using safe procedures, check if the PCB outputs voltage to the fan connector. If no voltage is present and fuses are intact, the control board may be defective.
• 5. Replace faulty components: Replace the fan assembly if the motor is defective. Replace the control board only with an original Junkers spare and have it configured by a qualified technician.