BoilerFaultCodesYour boiler is struggling to manage the internal water pressure, which is likely causing the system to shut down to prevent damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Expansion Vessel 12 Litre (Primary)
What causes this fault?
This fault occurs when the boiler's internal expansion vessel has failed or lost its air charge, leaving no room for water to expand as it heats up. The resulting surge in pressure often forces the safety valve to leak, which eventually leaves the system with too little water to operate safely. High pressure readings followed by the boiler losing pressure entirely are tell-tale signs of this component failing.
This issue often becomes apparent during the first cold spell of autumn when the heating is turned on for long periods, causing the water to expand more than it does in the summer.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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