BoilerFaultCodesYour boiler has detected an unusual and sudden temperature shift and has shut down as a safety precaution to prevent overheating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow and return sensor anomaly detected. Sudden temperature change detected on the flow or return sensor.
What causes this fault?
This fault occurs when the boiler's internal sensors detect an impossibly fast rise or fall in temperature, suggesting that water isn't moving through the unit correctly. The most common reason is a circulation failure, often caused by a faulty pump or a blockage in the pipework that prevents heat from being carried away from the heat exchanger.
This issue is more frequent when the heating is first turned on after summer, as pump components can seize up during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like 0A18 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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