BoilerFaultCodesYour boiler has switched itself off because it is getting too hot inside, usually to prevent internal damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Overheat thermostat tripped
What causes this fault?
This fault occurs when the internal temperature of the boiler rises above a safe limit, causing a safety sensor to cut the power. The most common reason is a blockage or a failing pump that prevents water from flowing through the system quickly enough to carry heat away from the burner. In some cases, it can also be triggered by a build-up of air or debris within the heat exchanger.
This issue often surfaces during the first cold spell of autumn when the heating is turned on after being dormant all summer, which can cause internal pump components to seize.
DIY fix possible
Check if your radiator valves are open to allow water to flow.Check the boiler pressure needle is in the green zone (between 1 and 1.5 bar).Press the 'Reset' button on the boiler controls to see if the fault clears after cooling down.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like E9 — no call-out fees, no surprises.
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Worcester Bosch Greenstar 25Si 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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