Error E5, furnace stops, sometimes accompanied by loud ignition or combustion noise

Safety first: Disconnect power and gas. Wait for the appliance to cool.

• 1. Inspect ionisation cable: Follow the cable from the electrode to the control board. Look for cracks, burn marks, or insulation damage. Replace if any defects are found.
• 2. Dry and clean electrode: Condensation or water ingress can cause false readings. Ensure the combustion chamber is dry. Clean the electrode and surrounding area.
• 3. Check connections: Reseat the ionisation cable connector on the PCB. Clean contacts with electrical contact cleaner if corroded.
• 4. Grounding check: Confirm that the burner and heat exchanger are properly grounded to the chassis. Tighten any loose screws or lugs.
• 5. Control board evaluation: If the electrode and cable are good but E5 persists, the flame detection circuit on the PCB may be faulty. Replacement of the control board should be done by an authorised Junkers technician.