Furnace locks out with E9, overheating indicated, unit very hot to touch

Safety first: Turn off power and gas. Do not reset repeatedly without finding the cause of overheating.

• 1. Allow cooling: Wait until the appliance cools down completely. Some overheat thermostats are manual reset; others reset automatically.
• 2. Check system pressure and air: Verify that the heating system pressure is within the range specified on the Junkers data plate (commonly 1.0–1.5 bar cold). Bleed radiators and the boiler's automatic air vent to remove trapped air.
• 3. Pump operation: With power restored, call for heat and listen/feel for the circulation pump running. If the pump is silent or very hot and not circulating, it may be seized or air-locked. Gently vent the pump via the bleed screw (if fitted) and try to free the shaft with a screwdriver as per manufacturer instructions.
• 4. Heat exchanger inspection: A heavily scaled or sludged heat exchanger can cause local overheating. Visual inspection and cleaning/descaling should be performed by a qualified technician.
• 5. Overheat thermostat check: Locate the safety temperature limiter on the flow pipe or heat exchanger. Check wiring and connectors. If it has a manual reset button, press it once after cooling. If it trips repeatedly, do not continue resetting—find and fix the root cause.
• 6. Professional service: Persistent E9 faults require a full hydraulic and combustion check by an authorised Junkers service partner.