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 system has become dangerously hot or the water pressure has dropped too low. The most common reason is a blockage or pump failure that prevents water from circulating correctly, causing the heat exchanger to exceed its safe operating limit. As a result, the boiler shuts down immediately to prevent any physical damage to the internal components.
This issue is more frequent in the autumn when heating systems are first turned on after summer, as pump seizing or air locks are common after 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.