Common problems guide

The most common Glow-worm Energy problems

The faults most likely to send a Glow-worm Energy 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.
41 documented codes
6 most common
1 DIY-safe checks
5 engineer needed

The 6 most common faults

01
F.22 High DIY-safe

Your boiler has stopped working because the amount of water circulating inside your heating system is currently too low.

What to try first

Locate the filling loop, which is a silver braided flexible hose with one or two valves attached under the boiler.Open the valves slowly to allow mains water into the system until the pressure gauge on the front display reaches between 1.0 and 1.5 bar.Close the valves tightly and turn the boiler off and on again to clear the error.

Est. cost
£80-120
Parts
Filling loop, Pressure relief valve, Pressure sensor
Full guide for F.22
02
F.00 High Engineer

Your boiler has lost the ability to accurately measure the temperature of the water flowing through the system, so it has shut down as a precaution to prevent overheating.

Est. cost
£120-220
Parts
NTC Temperature Sensor, Wiring harness
Full guide for F.00
03
F.01 High Engineer

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

Est. cost
£120-220
Parts
Return NTC thermistor
Full guide for F.01
04
F.10 High Engineer

Your boiler has detected a faulty connection in its temperature-monitoring system and has safely shut down to prevent overheating.

Est. cost
£120-220
Parts
NTC flow temperature sensor, Wiring harness
Full guide for F.10
05
F.11 High Engineer

Your boiler has detected a faulty connection in the part that measures the temperature of the water returning to the system, causing the boiler to shut down as a precaution.

Est. cost
£120-200
Parts
Return temperature sensor, Wiring harness
Full guide for F.11
06
F.20 High Engineer

Your boiler has automatically turned itself off because it has detected that its internal water temperature has become dangerously high.

Est. cost
£150-300
Parts
NTC Temperature Sensor, Pump, Heat Exchanger
Full guide for F.20
Parts most often replaced

on the Glow-worm Energy

Filling loopPressure relief valvePressure sensorNTC Temperature SensorWiring harnessReturn NTC thermistor

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 41-code list for the Glow-worm Energy

Related guides

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