Glow-worm Fuelsaver Complheat 40 55 Fault codes & diagnostics

6 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Regular Natural Gas 11.7-16.1 kW 1991-2002 Discontinued
Choose your boiler type

The Fuelsaver Compl range comes in 6 types

Pick the one you have. The fault codes, GC numbers and manual differ by type.

Fuelsaver Complheat 80 6 codes · 1 GC number Fuelsaver Complheat 55 6 codes · 1 GC number Fuelsaver Complheat 40 6 codes · 1 GC number Fuelsaver Complheat 65 6 codes · 1 GC number Spacesaver Complheat 60 6 codes · 1 GC number Spacesaver Complheat 70 6 codes · 1 GC number
Each model has its own manual A family spans several manuals, one per model or generation. Pick your model above and its page has the manual its fault codes were read from.

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
6 High
Just want the most common Glow-worm Fuelsaver Complheat 40 55 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 6 documented codes

Tap any card for details

Neon1

Your boiler has lost power or has insufficient water pressure to operate safely, meaning it cannot provide heating or hot water until reset.

High DIY-safe £90-280 Shared across the Fuelsaver Complheat 40 55 range

What to check first

  1. Check the pressure gauge on the front of the boiler or in your airing cupboard; if below 1.0 bar, top it up using the filling loop
  2. Check your home's consumer unit (fuse box) to ensure the heating circuit hasn't tripped
  3. Switch the boiler off at the wall, wait 30 seconds, and switch it back on to reset the electronics

Parts commonly replaced

  • PCB (Main Circuit Board)
  • Water Pressure Switch
  • Internal Glass Fuses

Related codes

Full explanation for Neon1
Neon2

Your boiler has switched itself off because it has become too hot internally, likely due to a circulation problem or a faulty safety sensor.

High DIY-safe £95-260 Shared across the Fuelsaver Complheat 40 55 range

What to check first

  1. Check that your pump is running and not stuck
  2. Ensure all radiator valves are open to allow water flow
  3. Once the unit has cooled, press the reset button located on the overheat thermostat (refer to manual for exact location)

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Water Differential Pressure Switch

Related codes

Full explanation for Neon2
Neon3

Your boiler has detected an issue with the ventilation system, meaning it cannot safely clear waste gases and has shut down as a precaution.

High Engineer only £150-350 Shared across the Fuelsaver Complheat 40 55 range

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Venturi tube

Related codes

Full explanation for Neon3
Neon4

Your boiler is attempting to start but cannot light or maintain the flame needed to provide heating and hot water.

High Engineer only £120-280 Shared across the Fuelsaver Complheat 40 55 range

Parts commonly replaced

  • Ignition electrode
  • Pilot injector
  • Gas valve
  • Flame sensing probe

Related codes

Full explanation for Neon4
RED NEON

Your boiler has stopped working because the water pressure in the central heating system is too low.

High DIY-safe £0-120 Shared across the Fuelsaver Complheat 40 55 range

What to check first

  1. Locate the external filling loop, which is usually a silver flexible hose with two small valves.
  2. Open both tap handles slowly until you hear water flowing into the system.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close both taps tightly.
  4. The red light should extinguish and the boiler should restart automatically.

Parts commonly replaced

  • Filling loop
  • Pressure gauge
  • Expansion vessel re-pressurisation
Full explanation for RED NEON
Red neon on fascia

Your boiler has stopped working because the water pressure in the central heating system is too low.

High DIY-safe £0-120 Shared across the Fuelsaver Complheat 40 55 range

What to check first

  1. Locate the filling loop, which is usually a silver flexible hose with one or two small taps.
  2. Slowly open the tap(s) until you hear water entering the system.
  3. Watch the pressure gauge and close the taps firmly once it reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for Red neon on fascia
Status & diagnostic codes

1 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

F1A Diagnostic Your boiler has stopped working because an internal safety fuse has blown, cutting off the electrical supply to the system.