BoilerFaultCodesTechnical description
Overheat fault
What causes this fault?
This fault occurs when the internal temperature sensors detect that the water inside the boiler has exceeded a safe limit, triggering an emergency shutdown to prevent damage. The most common reason is a failure in the circulation pump or a blockage in the pipework, which stops heat from being carried away from the burner quickly enough. It can also be caused by 'kettling' due to a build-up of limescale or sludge within the main heat exchanger.
This fault is more frequent in autumn when heating systems are first turned on after being dormant all summer, as pump components are more likely to 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.