Glow-worm Compact (2006-2011) Fault codes & diagnostics

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

CombiSystem Natural Gas 24 kW 1999-2003 Discontinued
GC Numbers 41-047-2647-047-0347-047-0447-047-0647-047-07

Replaced by: Flexicom

Download the Glow-worm Compact (2006-2011) manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
7 High 1 Low
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
41-047-26 Compact 100 System A 1999–2003
47-047-03 Compact 75p 1999–2002
47-047-04 Compact 80p 1999–2002
47-047-06 Compact 75e 1999–2003
47-047-07 Compact 80e 1999–2002
Just want the most common Glow-worm Compact (2006-2011) faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 8 documented codes

Tap any card for details

LED / flash-pattern codes
Low water pressure LED flash

Your boiler has detected that there is not enough water in the heating system to operate safely.

High DIY-safe £75-160

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath or near the boiler
  2. Slowly open the tap or taps on the filling loop to allow water into the system
  3. Monitor the pressure gauge until it reaches between 1 and 1.5 bar, then close the taps fully

Parts commonly replaced

  • Low water pressure switch
  • Filling loop
  • Expansion vessel
Full explanation for Low water pressure LED flash
Red flashing light (Flue)

Your boiler has detected a blockage in the exhaust pipe or a problem with the fan, causing the system to shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check the external flue pipe (the white pipe on your outside wall) for any visible obstructions like bird nests, leaves, or debris.
  2. Ensure there are no items such as garden furniture or plants blocking the airway of the flue.
  3. If the exterior is clear, do not attempt to open the boiler; you must call a Gas Safe engineer to inspect the internal fan and air pressure switch.

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Flue seals
Full explanation for Red flashing light (Flue)
Red flashing light (Gas)

Your boiler has stopped working because it cannot get a steady supply of gas to stay lit.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances, like a cooker, are working to confirm your gas supply is active.
  2. If you have a prepayment meter, check that you have enough credit.
  3. Locate your gas meter and ensure the main handle is in the 'on' position.
  4. Reset the boiler by turning the main selector dial to 'Reset' for five seconds, then back to your preferred setting.

Parts commonly replaced

  • Gas valve
  • Spark electrodes
  • Ignition lead
  • PCB
Full explanation for Red flashing light (Gas)
Digital codes
Mains LEDs

Your boiler has lost all power and is completely unresponsive because it is not receiving an electrical signal.

High Engineer only £150-350

Parts commonly replaced

  • Internal fuse
  • Printed Circuit Board (PCB)
Full explanation for Mains LEDs
Pilot does not stay alight

Your boiler's pilot light is failing to stay on because the internal sensor that detects the flame is either blocked, misaligned, or faulty, causing the boiler to shut off for safety.

High Engineer only £120-200

Parts commonly replaced

  • Thermocouple
  • Pilot burner assembly
Full explanation for Pilot does not stay alight
Pilot will not light

Your boiler is failing to ignite because it cannot start the small flame needed to fire up the main burner.

High Engineer only £120-250

Parts commonly replaced

  • Pilot injector
  • Piezo igniter
  • Ignition lead
  • Thermocouple
Full explanation for Pilot will not light
Red lockout light F

Your boiler has stopped working because the flame has extinguished unexpectedly, triggering a safety shutdown to prevent gas buildup.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe
  • PCB
Full explanation for Red lockout light F
Summer mode LED

Your boiler is failing to switch into summer mode due to an internal electronic circuit board failure.

Low Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
Full explanation for Summer mode LED
Status & diagnostic codes

15 operating states & engineer diagnostics

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

10 Diagnostic Your boiler is struggling to accurately read the water pressure in your heating system, which may prevent it from starting up reliably. 11 Diagnostic Your boiler's internal computer is experiencing a communication error, meaning it has safely shut itself down to prevent unpredictable operation. 12 Diagnostic Your boiler has developed an internal electrical fault that is preventing it from starting up or operating correctly. 13 Diagnostic Your boiler is failing to detect the gas flow required to ignite the flame, so it has shut itself down as a safety precaution. 14 Diagnostic Your boiler is struggling to detect the temperature of your hot water, which likely means you will have no hot water available until it is fixed. 15 Diagnostic Your boiler is struggling to detect the flow of water needed to provide your hot water and heating, so it has shut down to protect itself. 16 Diagnostic Your boiler has stopped working because an internal safety fuse has blown, cutting off the power to the main controls. 17 Diagnostic Your boiler has stopped working because an internal electrical fuse has blown, cutting off the power needed for it to operate. 18 Diagnostic Your boiler is failing to detect the airflow needed for safe operation, so it has shut down to prevent any unsafe combustion. 19 Diagnostic Your boiler has detected an issue with the internal component that helps control the fan, which is preventing the system from firing up safely. 20 Diagnostic Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely. 21 Diagnostic Your boiler is struggling to accurately measure the temperature of the water being sent to your radiators, so it has turned itself off as a precaution. 22 Diagnostic Your boiler has detected that it is struggling to remove trapped air from the system, which can prevent heat from circulating properly. F1 Diagnostic Your boiler has failed to ignite the flame, meaning it cannot produce any heat or hot water. F2 Diagnostic Your boiler has stopped working because an internal fuse has blown, preventing the system from receiving the electricity it needs to function.