Glow-worm Ci Range Fault codes & diagnostics

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

Combi Natural Gas 24-30 kW 2006-2010 Discontinued

Replaced by: Flexicom

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.
20 High
Just want the most common Glow-worm Ci Range faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 20 documented codes

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LED / flash-pattern codes
Red flashing light

Your boiler has encountered a general operation error and needs to be restarted to resume heating and hot water.

High DIY-safe £0-120

What to check first

  1. Locate the On/Off switch on the boiler control panel
  2. Turn the switch to the '0' position
  3. Wait for five seconds
  4. Turn the switch back to the 'I' position to reset the unit

Parts commonly replaced

  • Ignition Electrode
  • Printed Circuit Board (PCB)

Related codes

Full explanation for Red flashing light
Red flashing running lamp

Your boiler has lost water pressure and has shut down as a safety precaution.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath your boiler.
  2. Slowly open the tap or taps on the filling loop until you hear water entering the system.
  3. Monitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then turn the taps off tightly.
  4. The red light should stop flashing and the boiler should restart.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for Red flashing running lamp
Digital codes
0.5bar

Your boiler has lost water pressure and has shut down to prevent damage, meaning you will not have any heating or hot water until the system is topped up.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop, which is usually a flexible silver hose with two small taps underneath the boiler.
  2. Open both taps slowly until you hear water flowing and watch the pressure gauge rise.
  3. Close both taps firmly once the pressure gauge reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel
Full explanation for 0.5bar
01

Your boiler has stopped working because it cannot light the gas flame or it can't detect that the flame is lit.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to confirm gas supply.
  2. If you have a prepaid gas meter, ensure it has sufficient credit.
  3. Press the reset button on the boiler control panel once to see if it restarts.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 01
02

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

High Engineer only £120-£350

Parts commonly replaced

  • Air Pressure Switch
  • Fan Assembly
  • Venture Tube
Full explanation for 02
2.7bar

Your boiler has too much water inside it, causing the internal pressure to rise to an unsafe level.

High DIY-safe £80-160

What to check first

  1. Check that the filling loop valves are fully closed and not leaking
  2. Bleed water from a radiator using a radiator key to reduce the system pressure
  3. Monitor the pressure gauge until it returns to between 1.0 and 1.5 bar
  4. If pressure continues to rise on its own, turn off the water mains and call an engineer

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve (PRV)
Full explanation for 2.7bar
05

Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are open and not turned off.
  2. Ensure there is enough water pressure in the system (typically between 1 and 1.5 bar).
  3. Press the reset button on the control panel once the boiler has cooled down.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Main Heat Exchanger
Full explanation for 05
06

Your boiler has detected a problem with the sensor that measures the temperature of the water going to your radiators, causing the system to stop working for safety.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC thermistor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for 06
09

Your boiler has lost track of the system's water pressure because a sensing part has stopped working properly.

High Engineer only £120-190

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
Full explanation for 09
12

Your boiler's main control screens are having trouble talking to each other, which means the boiler doesn't know what settings you are asking for.

High DIY-safe £140-£320

What to check first

  1. Turn off the electrical power supply to the boiler at the fused spur switch.
  2. Wait approximately 60 seconds for the electronics to fully discharge.
  3. Turn the power back on to see if the communication link resets.

Parts commonly replaced

  • User Interface (Display Board)
  • Main Printed Circuit Board (PCB)
  • Communication Ribbons/Wiring
Full explanation for 12
Showing 11–20 of 20
13

Your boiler's internal computer has developed a fault and can no longer control the heating and hot water functions safely.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 13
14

Your boiler has become too hot and has shut down as a safety precaution to prevent damage.

High DIY-safe £100-£350

What to check first

  1. Check that your radiator valves are open to allow water to flow.
  2. Ensure there is enough pressure in the system by checking the gauge (it should be around 1.5 bar).
  3. Gently bleed your radiators to remove any trapped air that might be blocking circulation.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • NTC Thermistor
Full explanation for 14
15

Your boiler is unable to control the flow of gas required for ignition, meaning it cannot light to provide heat or hot water.

High Engineer only £180-280

Parts commonly replaced

  • Gas valve
  • Stepper motor assembly
  • Main PCB

Related codes

Full explanation for 15
16

Your boiler has detected a problem with the internal gas valve and has shut down as a safety precaution, meaning you will have no heating or hot water.

High Engineer only £180-320

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 16
17

Your boiler is receiving too little electricity from the mains supply to operate safely, causing it to shut down.

High Engineer only £100-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Regulator
Full explanation for 17
18

Your boiler's control panel has lost communication with the main computer, meaning you cannot adjust settings or operate the unit.

High Engineer only £180-350

Parts commonly replaced

  • User Interface PCB
  • Main Circuit Board (PCB)
  • Internal Ribbon Cable

Related codes

Full explanation for 18
19

Your boiler has stopped working because its internal temperature sensor has lost contact with the pipework or is failing to send a signal.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC Thermistor
  • Wiring clip
Full explanation for 19
20

Your boiler's internal control screen is unable to communicate properly with the main computer board, often after a recent repair or parts change.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB
  • User Interface Board
Full explanation for 20
F1

Your boiler is trying to start up but cannot detect a flame, causing the system to shut down for safety.

High DIY-safe £90-250

What to check first

  1. Check if other gas appliances (like a hob) are working to ensure gas supply is active
  2. Check that your credit is topped up if you have a pre-payment gas meter
  3. Press the 'Reset' button (indicated by a flame with a cross through it) and hold for 2 seconds

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve

Related codes

Full explanation for F1
F4

Your boiler is lighting up but quickly switching itself off because it cannot confirm that a flame is safely present.

High Engineer only £120-280

Parts commonly replaced

  • Flame sense electrode
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F4