BoilerFaultCodesYour boiler has reached an excessively high temperature 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 sensor above 95 °C
What causes this fault?
This fault occurs when the water leaving the boiler gets too hot, causing the system to shut down to prevent damage. The most common reason is a lack of water flow, often caused by a failing pump or a blockage in the pipework that prevents heat from being carried away from the boiler quickly enough.
This issue is more frequent during the first cold snap of autumn when heating systems are turned back on after sitting idle, which can cause internal pumps to seize.
DIY fix possible
Check that your radiator valves are open to allow water to circulateCheck that the system pressure is between 1.0 and 1.5 bar on the gaugeTurn the boiler off and wait 30 minutes for it to cool down before resetting
Find a Gas Safe engineer
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A boiler cover plan would cover faults like b18 — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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