BoilerFaultCodesGlow-worm 0.5bar Fault Code
Also written as 05BAR — same fault.
The Glow-worm 0.5bar fault code means: your boiler has lost water pressure and has shut down to prevent damage, meaning you currently have no heating or hot water.. It appears on 3 Glow-worm models in our database.
Technical description: Lack of water fault (<0.5b)
What causes the Glow-worm 0.5bar fault?
This fault occurs when the water pressure inside your heating system drops below a safe operating level, causing the boiler to shut down to protect the internal components. The most common reasons are a small leak somewhere in your pipework or radiators, or the pressure being manually drained during recent maintenance without being refilled.
This issue is frequently seen in autumn when homeowners turn their heating back on for the first time, as the change in temperature can highlight small leaks or air pockets that developed over the summer.
DIY fix possible
Locate the filling loop (usually two blue or black levers) underneath the boiler.Slowly open both levers until you hear water flowing and the pressure gauge rises.Close both levers tightly once the gauge reaches 1.5 bar.
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Gas Safe Register →Glow-worm models that show the 0.5bar fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 0.5bar 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