BoilerFaultCodesYour boiler has paused operation because an external safety device or control, such as a thermostat or pump, has disconnected the circuit.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: External interlock circuit open - boiler shuts down and will restart when the circuit is closed
What causes this fault?
This fault occurs when an external control or safety device breaks the electrical circuit, telling the boiler to stop running for safety reasons. The most common reason is a faulty room thermostat or a loose wiring connection between the boiler and its external controls. In some cases, it can also be triggered if an external pump has failed or disconnected.
This issue often surfaces at the start of autumn when homeowners turn their heating on for the first time in months and discover their wall thermostat has failed or has dead batteries.
DIY fix possible
Check if your room thermostat or programmer is turned up and has powerReplace batteries in your wireless room thermostat if applicableEnsure any external switches or emergency shut-off buttons haven't been accidentally knocked
Find a Gas Safe engineer
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A boiler cover plan would cover faults like 9 — 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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