BoilerFaultCodesTechnical description
High limit thermostat signalising overheating. Check the valve of the radiators in the heating, check if the Combi boiler water pressure is low, if it is then the heating circuit needs filling with water
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to shut the system down to prevent damage. The most common reasons are a lack of water pressure to move heat away from the burner, or a mechanical blockage like a stuck pump or closed radiator valves preventing the water from circulating.
This issue is frequently seen in autumn when the heating is turned on for the first time after summer, as pump components can seize during long periods of inactivity.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.