BoilerFaultCodesYour boiler is struggling to circulate water quickly enough through your pipes, which is causing it to stop 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: Microbore system or pump speed setting fault
What causes this fault?
This fault occurs when the boiler detects that water isn't moving through the system fast enough to carry heat away from the heat exchanger. The most common reasons are a failing internal pump that has lost its pushing power or a blockage in the narrow pipework that is restricting flow. When the water sits still for too long, it overheats rapidly, forcing the boiler to shut down for safety.
This issue is most frequently noticed when the heating is first turned on in autumn, as pump components can seize up or sludge can settle during the summer months of inactivity.
DIY fix possible
Ensure all radiator valves (TRVs) are fully open to allow water to flow.Check that the boiler pressure is between 1 and 1.5 bar on the gauge.Gently bleed your radiators to remove any trapped air pockets.
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A boiler cover plan would cover faults like F8 — 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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