BoilerFaultCodesYour boiler has detected that the water temperature is too high and has shut down to prevent damage to its internal components.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Fault flow sensor over temperature – flow sensor flow/return line probe differential alarm
What causes this fault?
This fault occurs when the boiler's sensors detect that water is heating up far too quickly or staying too hot compared to the return flow. The most common reason is a circulation failure, often caused by a seized pump or a blockage in the heat exchanger that prevents water from moving through the system. It can also be triggered by a faulty sensor sending an incorrect temperature reading to the main control board.
This fault is more common in autumn when homeowners first turn their heating back on, as circulation pumps can often seize up after being idle during the summer months.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like 4070 — no call-out fees, no surprises.
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