BoilerFaultCodesYour boiler has detected that hot water is escaping through the safety overflow pipe, usually because the system is overheating or a valve has failed.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Hot water fault over-flow pipe
What causes this fault?
This fault occurs when the internal pressure within your boiler gets too high, forcing the safety valve to open and release water to prevent damage. The most common reasons are a loss of air in the expansion vessel or a buildup of limescale preventing the safety valve from closing properly. Since the system has lost water and pressure, the boiler shuts down to protect itself from overheating.
This issue often surfaces in autumn when the heating is turned on for the first time after summer, as the expansion vessel may have lost its charge during the months of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like G9 — no call-out fees, no surprises.
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