BoilerFaultCodesGlow-worm F10 Fault Code
The Glow-worm F10 fault code means: your boiler has detected that its temperature sensors are incorrectly placed or wired, preventing it from calculating how much heat is being delivered to your home.. It appears on 10 Glow-worm models in our database.
Technical description: Flow and return thermistors reversed.
What causes the Glow-worm F10 fault?
This fault occurs when the boiler's control board detects that the temperature readings from the internal pipework are coming back in the wrong order. The most common reason is that the flow and return sensors have been physically clipped onto the wrong pipes or the wiring connectors have been swapped during a previous repair. Because the boiler cannot accurately monitor how heat is moving through the system, it shuts down as a safety precaution.
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 F10 fault code
Click a model for the full fault code list and model-specific repair notes.
- Flexicom 18sx Repair: £90-160
- Flexicom hx Repair: £90-160
- Flexicom sx Repair: £90-160
- Ultracom 2 CXI Repair: £90-160
- Ultracom 2 HXI Repair: £90-160
- Ultracom 24cx 30cx Repair: £90-160
- Ultracom 35 Store Repair: £90-160
- Ultracom cxi Repair: £90-160
- Ultracom hxi Repair: £90-160
- Xtramax HE Repair: £90-180
Source
Glow-worm F10 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