Furnace starts but shuts down after a few minutes, with noticeable overheating of the casing.

Safety: Allow the furnace to cool before touching pipework or internal components.

• Check system valves: Ensure all isolation valves around the furnace and main circuits are fully open.
• Bleed air: Bleed radiators and any automatic air vents. Listen for gurgling sounds that indicate trapped air.
• Check pump operation: Place a screwdriver tip on the pump body and your ear on the handle to listen for running noise. If silent or noisy, the pump may be stuck.
• Schedule cleaning: Have a technician clean the primary heat exchanger if there is evidence of scale or sludge.