BoilerFaultCodesTechnical description
The boiler is fitted with a safety thermostat to protect against overheating of the water. Should the boiler fail to light, allow it to cool and press the reset button.
What causes this fault?
This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety switch to cut the power. The most common reasons are a failed pump that isn't moving water around the system quickly enough or a blockage in the pipework caused by a build-up of sludge. It can also happen if the external controls fail to tell the boiler to turn off once the house is warm.
This issue often surfaces during the first cold spell of autumn when the heating system is turned back on after being idle all summer, which can cause internal parts like the pump to seize.
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.