BoilerFaultCodesTechnical description
The safety cut-out in the primary heat exchanger is defective
What causes this fault?
This fault occurs when the boiler's internal safety switch detects that the main heat exchanger is getting too hot, or if the sensor itself has failed and is sending incorrect data. The most common reasons include a lack of water flow caused by a trapped air bubble, a failing pump, or a build-up of sludge that prevents heat from being transferred away from the unit quickly enough.
This fault is more common in autumn when heating systems are first turned on after a long summer break, as internal pumps can seize up or air can become trapped in the pipes.
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.