BoilerFaultCodesYour boiler has temporarily stopped because water is not moving through the system quickly enough, causing it to overheat too fast.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Shut the boiler down in a blocking mode for 10 minutes (insufficient water flow, flow/return dt > 22°C or a rate of rise in the flow temperature > 1°C/sec)
What causes this fault?
This fault occurs when heat cannot be carried away from the boiler's heat exchanger quickly enough, leading to a sudden and dangerous spike in temperature. The most common reasons include a failing internal pump that isn't pushing water round the house, or a buildup of sludge and debris that has restricted the flow within the pipes. When the system detects that the water is getting too hot too fast, it shuts down to prevent the components from melting or cracking.
This issue often surfaces during the first few cold days of autumn when the heating is turned back on after being idle all summer, which can cause internal pump components to seize.
DIY fix possible
Check that all radiator valves (TRVs) are fully openEnsure your system pressure is topped up to between 1 and 1.5 barCheck that the external pump or any isolation valves are in the open position
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A boiler cover plan would cover faults like 9 — no call-out fees, no surprises.
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