BoilerFaultCodesYour boiler has detected that the water is heating up too quickly, which usually means it can't circulate water through the system properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Excessive temperature rise
What causes this fault?
This fault occurs when the heat inside the boiler builds up much faster than the water can carry it away. The most common reason is a blockage or a failing pump preventing the water from flowing through the pipes and radiators effectively. It can also be caused by a build-up of sludge or debris inside the main heat exchanger, which restricts the water path.
This fault is frequently seen at the start of autumn when heating systems are turned back on after being idle all summer, which can cause internal pump parts to seize.
DIY fix possible
Check that your radiator valves are open and not turned to zero.Ensure your boiler pressure is between 1 and 1.5 bar on the gauge.Try resetting the boiler to see if the fault clears.
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A boiler cover plan would cover faults like b25 — no call-out fees, no surprises.
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