BoilerFaultCodesYour boiler is shutting down because it is getting too hot too quickly, likely due to a water circulation problem.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Heat exchanger blocked or pump failure (Flow/Return Delta T too high).
What causes this fault?
This fault happens because water is not moving through the boiler fast enough to carry heat away, causing the internal temperature to spike instantly. The most common reasons are a broken internal pump that can't push the water or a buildup of sludge and scale that has physically blocked the narrow channels inside the heat exchanger.
This issue often comes to light during the first cold spell 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 your radiator valves are openEnsure the system pressure is between 1.0 and 1.5 barGently bleed your radiators to remove trapped air
Find a Gas Safe engineer
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A boiler cover plan would cover faults like F3 — no call-out fees, no surprises.
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Glow-worm Xtramax HE is discontinued — time for a new one?
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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