BoilerFaultCodesGlow-worm F81 Fault Code
The Glow-worm F81 fault code means: your boiler is struggling to heat up water for your taps because the internal pump or sensor that manages hot water is not working correctly.. It appears on 6 Glow-worm models in our database.
Technical description: Domestic hot water pump/loading fault
What causes the Glow-worm F81 fault?
This fault occurs when the boiler detects that water is not being heated quickly enough for your taps, often because the internal pump has seized or failed. It can also be triggered by a buildup of limescale or debris in the heat exchanger, which restricts water flow and prevents the system from transferring heat effectively. Essentially, the boiler is shutting down because it cannot move the hot water out of the unit fast enough to avoid overheating.
This issue is more frequently reported in winter when the incoming cold water temperature drops, forcing the boiler to work harder and highlighting any existing blockages or pump weaknesses.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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 F81 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F81 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