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 unit is operating outside of its safe temperature or combustion limits. It is typically triggered because the system has overheated or failed to ignite correctly, forcing the boiler to shut down to prevent damage. The most common reasons include a failing limit thermostat, a blocked heat exchanger, or an issue with the gas supply components.
This fault is more frequent during the first cold snap of autumn when boilers are switched back on after being idle, as internal mechanical parts like the gas valve can become stuck.
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.