Furnace shuts down with overheat indication, flow temperature rises rapidly then burner cuts out

Safety: Isolate power and allow the appliance to cool fully before touching any internal components.

• Check system pressure: For sealed Baxi systems, verify that the system pressure gauge is within the recommended range (typically 1.0–1.5 bar when cold). Repressurise via the filling loop if low.
• Bleed radiators and air vents: Remove trapped air from radiators and any automatic air vents to restore circulation.
• Verify pump operation: With power restored, call for heat and feel the Baxi circulation pump. It should vibrate slightly and the flow pipe should gradually warm. If the pump is silent or extremely hot but not pumping, it may be seized or airlocked.
• Clean system filter: If a Baxi magnetic filter or system strainer is installed, isolate and clean it to remove sludge that may restrict flow.

Professional tasks: Descaling or replacing a blocked primary heat exchanger, replacing the pump, or testing/replacing the overheat thermostat should be done by a heating engineer.