BoilerFaultCodesYour boiler has detected that the water temperature has risen too quickly or reached an unusually high level, causing it to shut down 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: Actual temperature: Flow temperature at the flow temperature sensor
What causes this fault?
This fault occurs when water cannot travel through the boiler’s heat exchanger fast enough to carry the heat away, causing a rapid temperature spike. The most common reasons are a failed internal pump, a blockage caused by sludge or debris in the pipework, or air trapped within the system preventing proper circulation.
This issue often surfaces during the first cold spell of autumn when the heating is turned on after being idle all summer, which can cause internal pump parts to seize.
DIY fix possible
Check that all radiator valves are fully open to allow water to flow.Ensure the system pressure gauge is between 1.0 and 1.5 bar.Try resetting the boiler via the display panel to see if the fault clears.
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A boiler cover plan would cover faults like A-A5 — 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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