BoilerFaultCodesYour boiler has temporarily stopped providing heating or hot water because an external control or smart accessory is preventing it from firing up.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Accesory Module is blocking burner operation
What causes this fault?
This fault occurs when an external device connected to the boiler, such as a smart thermostat or a wireless receiver, sends a signal to stop the burner from firing. The most common reason is a loss of communication between your thermostat and the boiler, often caused by dead batteries or a signal interference. Essentially, the boiler is waiting for a 'go' signal from your controls that never arrives or is being actively blocked.
DIY fix possible
Check your external thermostat or smart home app to ensure the heating is actually turned on.Replace the batteries in your room thermostat or programmable controller.Restart your internet router if you use a smart heating system like Hive, Nest, or MiGo.
Find a Gas Safe engineer
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like S.42 — no call-out fees, no surprises.
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Glow-worm Flexicom cx 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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