Red flashing running lamp High

Glow-worm Red flashing running lamp Fault Code

Also written as REDFLASHINGRUNNINGLAMP — same fault.

The Glow-worm Red flashing running lamp fault code means: your boiler has lost water pressure and has shut down as a safety precaution.. It appears on 1 Glow-worm model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 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 the Glow-worm Red flashing running lamp 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.

Typical repair cost £0-120 (including labour)

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.

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Glow-worm models that show the Red flashing running lamp fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Glow-worm Red flashing running lamp fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026