BoilerFaultCodesYour boiler has detected that water is circulting poorly or heating up too quickly, causing the temperature sensors to provide unusual readings.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow/return sensor temperature test
What causes this fault?
This fault occurs when the boiler's sensors detect that the water temperature is rising too quickly or behaving erratically, suggesting the water isn't moving through the system properly. The most common reasons are a failing internal pump that can't push the water around, or a blockage within the heat exchanger. It can also be caused by air trapped in the pipework or sensors that have become faulty and are providing incorrect data to the control board.
This issue is more frequent in autumn when the heating is first turned on after summer, as internal pump parts can seize during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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