BoilerFaultCodesTechnical description
The contacts of the safety temperature sensor have been interrupted
What causes this fault?
This fault occurs when the boiler's internal safety switch detects that the heat exchanger has reached an unsafe temperature, causing the system to shut down to prevent damage. The most common reason is a lack of water flow through the unit, often caused by a failing pump, a blockage in the pipework, or air trapped within the heat exchanger. It can also be triggered if the wiring connecting the sensor to the main control board becomes loose or damaged.
This fault is more common when the heating is first turned on after autumn, as pump blockages often occur after long periods of inactivity during the 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.