BoilerFaultCodesYour boiler is receiving power but failing to start when you ask for heating or hot water, likely due to a faulty external control or internal communication issue.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Boiler not operating during central heating demand (HW ok) or hot water demand (CH ok) or during any demand. Possible solution/check: External diverter valve, External timer or room stat, Temperature control in frost protection position, Live demand at ST10-LR, Facia mounted timer, Control board, Short circuit across ST8.
What causes this fault?
This issue occurs when your boiler is receiving electrical power but isn't getting the instruction to start, often because a signal from your external thermostat or timer is being blocked. It usually means a physical part like a motor or a switch has failed, preventing the boiler from knowing that you have actually turned the heating or hot water on.
This fault often becomes apparent during the first cold spell of autumn when heating systems are switched back on after being idle all summer, which can cause internal moving parts to seize.
DIY fix possible
Check that your room thermostat and programmer are turned up and set to 'on'.Ensure the temperature control dial on the boiler front is turned up and not set to the frost protection position.Replace the batteries in your wireless room thermostat if applicable.
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