BoilerFaultCodesTechnical description
The safety devices have been activated (lockout)
What causes this fault?
This fault occurs when the boiler's internal temperature or pressure exceeds safe limits, triggering a total system shutdown to prevent damage. It is usually caused by a failure in the circulation pump or a blockage within the heat exchanger that stops water from moving through the unit quickly enough. When the water stays still for too long, it overheats almost instantly, causing the safety sensors to trip.
This issue is more frequent in autumn when the heating is first switched back on after a long summer break, as internal pumps 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.