BoilerFaultCodesTechnical description
Safety temperature limiter in heat exchanger or flue gas temperature limiter has been activated.
What causes this fault?
This fault occurs when the internal temperature of the boiler rises above a safe limit, causing the system to shut down to prevent damage. The most common reasons are a lack of water flow due to a seized pump, a blockage in the heat exchanger, or air trapped within the pipework. Effectively, the heat being produced by the burner is not being carried away into your radiators quickly enough.
This fault often appears during the first cold spell of autumn when the heating is turned on after a long summer break, as internal pump components can seize during 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.