BoilerFaultCodesYour boiler has lost water pressure and has shut down as a safety precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: 18si Only • If the boiler loses water: the pressure will be indicated, see diagram 1 (a) and the running lamp (b) will flash red indicating a fault.
What causes this fault?
This fault occurs when the water level inside the central heating system drops below a safe threshold, often due to a small leak in the pipework or a radiator. It can also happen if air has been bled from the radiators recently or if the internal expansion vessel has lost its charge, causing water to escape through the safety valve. Without enough water pressure, the boiler cannot circulate heat safely and shuts down to prevent the heat exchanger from overheating.
This issue often surfaces at the start of autumn when the heating is turned on for the first time after summer, as the change in temperature reveals small leaks or pressure losses.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) underneath your boiler.Slowly open the tap or taps on the filling loop until you hear water entering the system.Monitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then turn the taps off tightly.The red light should stop flashing and the boiler should restart.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like Red flashing running lamp — no call-out fees, no surprises.
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Glow-worm 18si 24ci 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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