BoilerFaultCodesYour boiler has detected that the water temperature is changing too quickly or inconsistently, causing it to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Variation on temperature of primary and/or return too high
What causes this fault?
This fault occurs when the internal sensors detect the water temperature within the boiler is rising too rapidly or behaving erratically. This is usually caused by a blockage or a pump failure that prevents water from flowing through the system quickly enough to carry the heat away.
This issue often surfaces in autumn or winter when the heating is first turned on after being idle, as pump components can seize during the summer months.
DIY fix possible
Check that all radiator valves are fully openEnsure the central heating system pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air
Find a Gas Safe engineer
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like AL74 — 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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