Thermostat displays E05 and cannot control the heating zone valve or pump; zone remains off

Safety: Isolate mains power to the boiler and any external pumps/valves before working on wiring. Risk of electric shock.

• Step 1 – Visual inspection: Remove the thermostat from its base. Inspect the heating output terminals (e.g., COM/NO) for signs of burning or melted plastic.
• Step 2 – Disconnect load: Temporarily disconnect the wires going to the pump or zone valve from the thermostat output. Restore power and see if E05 clears. If it does, the external load is likely faulty.
• Step 3 – Check pump/valve: Have a technician test the circulation pump or zone valve coil for correct resistance and insulation. Replace any component that is shorted or drawing excessive current.
• Step 4 – Verify wiring: Ensure that the thermostat output is not directly switching a high-current load beyond its rating. For larger pumps, use an external relay or Immergas zone control module as specified.
• Step 5 – Replace thermostat or relay module: If E05 persists with no load connected, the internal relay or output driver on the thermostat is damaged and the thermostat or its relay module must be replaced.