Common problems guide

The most common Glow-worm Flexicom hxi problems

The faults most likely to send a Glow-worm Flexicom hxi into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
8 documented codes
6 most common
1 DIY-safe checks
5 engineer needed

The 6 most common faults

01
F22 High DIY-safe

Your boiler has stopped because the water pressure inside the heating system has dropped too low to operate safely.

What to try first

Locate the external filling loop, which is a flexible silver hose connected to the pipework underneath the boiler.Open the two valves at either end of the filling loop to allow water into the system, watching the pressure gauge on the front of the boiler.Once the needle reaches the green zone (typically between 1.0 and 1.5 bar), tightly close both valves and ensure no water is leaking from the loop.

Est. cost
£80-150
Parts
Pressure relief valve, Pressure sensor, Expansion vessel
Full guide for F22
02
F4 High Engineer

Your boiler has stopped working because it is unable to accurately measure the temperature of the water returning to it from your radiators.

Est. cost
£120-220
Parts
Return thermistor sensor, Wiring harness
Full guide for F4
03
F6 High Engineer

Your boiler's main control panel is having trouble communicating with the internal computer system, preventing the unit from starting safely.

Est. cost
£150-300
Parts
UI interface harness, Main printed circuit board (PCB)
Full guide for F6
04
F10 High Engineer

Your boiler has detected that the electricity supply reaching it is too low to operate safely, causing it to shut down to prevent damage.

Est. cost
£120-250
Parts
Printed Circuit Board (PCB), Power supply wiring/fused spur
Full guide for F10
05
F13 High Engineer

Your boiler is struggling to get rid of the wastewater it produces, causing it to block its exhaust system as a safety precaution.

Est. cost
£120-250
Parts
Condensate siphon, Air pressure switch, Condensate trap
Full guide for F13
06
F25 High Engineer

Your boiler has detected that water is not circulating through your heating system correctly, causing it to overheat and shut down for safety.

Est. cost
£150-350
Parts
Central Heating Pump, System Filter, Diverter Valve
Full guide for F25
Parts most often replaced

on the Glow-worm Flexicom hxi

Pressure relief valvePressure sensorExpansion vesselReturn thermistor sensorWiring harnessUI interface harness

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Glow-worm shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 8-code list for the Glow-worm Flexicom hxi

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →