BoilerFaultCodesYour boiler has sensed it is getting too hot and has shut itself down as a safety precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Limit thermostat (STB) has triggered
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, forcing the system to shut down to prevent damage. The most common reasons are a pump failure that stops water from moving around the system or a build-up of debris causing a blockage in the heat exchanger.
This issue is more frequent during the autumn when heating is turned back on after a long summer break, as internal components like the pump can seize from lack of use.
DIY fix possible
Check that your radiator valves are open and not turned offEnsure there is enough water pressure in the system by checking the pressure gaugePress the reset button on the front of the boiler control panel
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like E9 — no call-out fees, no surprises.
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Worcester Bosch WR325 RSF 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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