BoilerFaultCodesTechnical description
The safety devices have been activated (lockout)
What causes this fault?
This fault occurs when the boiler's internal safety sensors detect that the temperature has exceeded safe operating limits, triggering an immediate shutdown to protect the system. The most common reason is a restriction in water flow or a failure in the components that monitor heat, such as a faulty limit thermostat or a malfunctioning control board.
This issue is more frequent during the first cold snap of autumn when a heating system is turned on for the first time after months of inactivity, often revealing pump stickiness or airlocks.
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.
Find a Gas Safe engineer
Search the official register →