BoilerFaultCodesGlow-worm 0 bar Fault Code
Also written as 0BAR — same fault.
The Glow-worm 0 bar fault code means: your boiler has lost its water pressure, which means it has stopped running to protect the internal components from damage.. It appears on 3 Glow-worm models in our database.
Technical description: Indicates 0 bar pressure in the system on the display
What causes the Glow-worm 0 bar fault?
This fault occurs when the water level inside your central heating system drops too low for the boiler to operate safely. It is usually caused by a small leak in the pipework or radiators, or because air was recently bled from the system without being topped back up.
This issue is more common in autumn when homeowners turn their heating back on for the first time, exposing small leaks or air pockets that developed over the summer.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) under the boiler.Slowly open the one or two small taps on the hose until you hear water flowing.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps tightly.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Glow-worm models that show the 0 bar fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 0 bar 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