BoilerFaultCodesGlow-worm F.89 Fault Code
Also written as F89 — same fault.
The Glow-worm F.89 fault code means: your boiler's internal pump is not moving water around the system correctly, which has caused the boiler to stop working to prevent overheating.. It appears on 6 Glow-worm models in our database.
Technical description: Pump fault
What causes the Glow-worm F.89 fault?
This fault occurs when the boiler's internal pump fails to circulate water, leading to a build-up of heat that triggers a safety shutdown. The most common reasons are a mechanical failure of the pump motor, a build-up of sludge or debris blocking the internal components, or a communication issue between the pump and the main control board.
This fault is more frequent in autumn or early winter when pumps that have been idle over the summer become 'stuck' or seized when the heating is first switched back on.
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 F.89 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F.89 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