Glow-worm Fuelsaver Complheat 40 55 Fault codes & diagnostics

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

Regular Natural Gas 11.7-16.1 kW 1994-1996 Discontinued
GC Number 41-313-25

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10 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 10 documented codes

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Neon 1 NOT lit

Your boiler is not receiving electrical power or has shut down because there is not enough water pressure in the system.

High DIY-safe £90-250

What to check first

  1. Check that the boiler's main power switch is turned on.
  2. Check your home's consumer unit (fuse box) to see if a circuit has tripped.
  3. Check the pressure gauge and, if below 1 bar, use the filling loop to top up the water pressure.

Parts commonly replaced

  • PCB Fuse
  • Low Water Pressure Switch
  • Printed Circuit Board (PCB)
Full explanation for Neon 1 NOT lit
Neon 2 NOT lit

Your boiler has shut itself down because it became too hot, likely due to a circulation problem or a component failure.

High DIY-safe £100-280

What to check first

  1. Locate the manual reset button on the overheat thermostat (usually behind the front panel or at the bottom).
  2. Press the button to reset the boiler once the unit has cooled down.
  3. Ensure all radiator valves are open and your heating system pump is running.

Parts commonly replaced

  • Overheat Thermostat
  • Central Heating Pump
  • Water Differential Pressure Switch

Related codes

Full explanation for Neon 2 NOT lit
Neon 3 NOT lit

Your boiler has stopped working because it cannot confirm that the internal fan is safely clearing waste gases from the system.

High Engineer only £120-£280

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Venturi tube

Related codes

Full explanation for Neon 3 NOT lit
Neon 4 NOT lit

Your boiler is failing to light its pilot light or detect a steady flame, meaning it cannot start the heating process.

High Engineer only £120-280

Parts commonly replaced

  • Thermocouple
  • Pilot Burner
  • Gas Valve
  • Ignition Lead
Full explanation for Neon 4 NOT lit
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

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

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

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

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

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

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