Technical description
Overtemperature protection intervention
What causes this fault?
This fault occurs when the internal temperature of the boiler rises above a safe limit, usually because water isn't moving through the system fast enough to carry heat away. The most common reasons are a failing circulation pump, a build-up of sludge or limescale blocking the heat exchanger, or a 'pocket' of air trapped within the unit.
This fault is frequently seen when the heating is first turned on after autumn, as pump components can seize up during months 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.