BoilerFaultCodesTechnical description
Over heat cut off activated | Maximum temperature exceeded
What causes this fault?
This fault occurs when the water inside the boiler reaches a temperature that is dangerously high, triggering a safety shut-off. This is usually caused by a pump failure, a blockage in the pipework, or a build-up of sludge that prevents heat from moving away from the internal heat exchanger. Effectively, the heat is being generated but has nowhere to go, causing the system to protect itself by locking out.
This fault is frequently seen at the start of autumn when heating systems are turned on for the first time in months, as pump components can seize up after being idle all summer.
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.