BoilerFaultCodesGlow-worm 09 Fault Code
The Glow-worm 09 fault code means: your boiler has lost track of the system's water pressure because the internal sensor is failing or disconnected, causing the unit to shut down for safety.. It appears on 7 Glow-worm models in our database.
Technical description: Water pressure sensor fault
What causes the Glow-worm 09 fault?
This fault occurs when the boiler's internal computer can no longer read the water pressure inside the system. The most common reason is that the pressure sensor has developed an electrical failure or has become blocked with sludge and debris, preventing it from sending a signal. Because the boiler cannot confirm there is enough water to operate safely, it shuts down to prevent the unit from overheating.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Glow-worm models that show the 09 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 09 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