Glow-worm 30ci Plus Fault codes & diagnostics

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

Combi Natural GasLPG 30 kW 2005-2009 Discontinued
GC Number 47-019-03

Replaced by: Flexicom cx

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 33 High 5 Medium
Just want the most common Glow-worm 30ci Plus faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 39 documented codes

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0.5bar

Your boiler has lost water pressure and has shut down to prevent damage, meaning you currently have no heating or hot water.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually two blue or black levers) underneath the boiler.
  2. Slowly open both levers until you hear water flowing and the pressure gauge rises.
  3. Close both levers tightly once the gauge reaches 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for 0.5bar
01

Your boiler has stopped working because it cannot light the gas burner to provide heating or hot water, usually because the gas supply is interrupted or the ignition spark has failed.

High DIY-safe £120-350

What to check first

  1. Check if your gas meter has credit or if other gas appliances in your home are working.
  2. Ensure the blue gas isolation valve under the boiler is in the 'open' position (aligned with the pipe).
  3. Press the 'Reset' button (indicated by a flame with a line through it) and hold for one second.

Parts commonly replaced

  • Ignition electrode
  • Lead assembly
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 01
02

Your boiler has stopped working because the fan isn't starting up to safely clear waste gases from the system.

High Engineer only £120-£350

Parts commonly replaced

  • Fan unit
  • Air pressure switch
  • Main PCB

Related codes

Full explanation for 02
2.7bar

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

Medium DIY-safe £60-180

What to check first

  1. Check that the filling loop valves are tightly closed
  2. Bleed water from a radiator using a bleed key to reduce pressure
  3. Monitor the pressure gauge to ensure it returns to between 1.0 and 1.5 bar
  4. Reset the boiler once the pressure is within the normal range

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve (PRV)

Related codes

Full explanation for 2.7bar
03

Your boiler has detected an issue with how it moves air and waste gases through the system, causing it to shut down for safety.

High Engineer only £100-£350

Parts commonly replaced

  • Fan
  • Air pressure switch
  • Flue seals
  • Venture tube

Related codes

Full explanation for 03
04

Your boiler has stopped working because it cannot light the gas needed to provide heating and hot water.

High DIY-safe £100-350

What to check first

  1. Check if your gas supply is turned on at the meter
  2. Check if other gas appliances, like a hob, are working correctly
  3. Press the reset button (indicated by a flame with a line through it) for five seconds

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 04
05

Your boiler has shut down because it has detected it is getting too hot, usually due to a lack of water flow or a circulation blockage.

High DIY-safe £120-350

What to check first

  1. Check if your radiator valves are open to ensure water can circulate.
  2. Check the boiler pressure gauge and top it up to 1.5 bar if it is low.
  3. Gently press the reset button on the front of the boiler.

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat (Limit stat)
  • Main heat exchanger

Related codes

Full explanation for 05
06

Your boiler has stopped working because a sensor that measures the temperature of the water leaving the unit has failed or has a poor connection.

High Engineer only £90-160

Parts commonly replaced

  • Central heating flow NTC thermistor
  • Wiring harness / Connector

Related codes

Full explanation for 06
07

Your boiler is struggling to accurately measure the temperature of your hot water due to a faulty internal sensor.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC thermistor
  • Connecting wiring harness

Related codes

Full explanation for 07
08

Your boiler has detected a problem with the sensor that monitors the temperature of its internal hot water store.

Medium Engineer only £90-180

Parts commonly replaced

  • Micro-accumulation NTC sensor
  • Wiring harness

Related codes

Full explanation for 08
Showing 11–20 of 39
09

Your boiler has lost the ability to monitor its own water pressure, meaning it has shut down to prevent damage even if there is enough water inside.

High Engineer only £130-190

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness connector

Related codes

Full explanation for 09
10

Your boiler has stopped working because a sensor that monitors the temperature of the water returning from your radiators has developed a fault.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Return NTC Sensor
  • Connecting Wiring Loom

Related codes

Full explanation for 10
12

Your boiler is having trouble communicating with the control panel or your thermostat, meaning it cannot receive your instructions to turn on.

High Engineer only £120-280

Parts commonly replaced

  • User Interface PCB
  • Wiring Harness
  • External Thermostat

Related codes

Full explanation for 12
13

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

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for 13
14

Your boiler has reached an unsafe temperature and has shut itself down to prevent damage or overheating.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar.
  3. Reset the boiler using the power button or reset switch and see if the fault clears.

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Main heat exchanger (flushing/cleaning)

Related codes

Full explanation for 14
15

Your boiler is unable to control the gas flow properly, which is preventing it from lighting to provide heating or hot water.

High Engineer only £180-320

Parts commonly replaced

  • Gas valve
  • Wiring harness
  • Main PCB

Related codes

Full explanation for 15
16

Your boiler has detected a problem with how gas flows into the unit, meaning it has shut down for safety to prevent a gas-related issue.

Emergency Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for 16
17

Your boiler has stopped working because the electrical power coming from your mains supply has dropped too low for it to run safely.

High Engineer only £100-280

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Regulator

Related codes

Full explanation for 17
18

Your boiler's control panel and its main computer are having trouble communicating with each other, meaning you cannot change settings or see the boiler's status correctly.

High Engineer only £180-350

Parts commonly replaced

  • User Interface (Display PCB)
  • Main Printed Circuit Board (PCB)
  • Internal Wiring Harness
Full explanation for 18
19

Your boiler has detected that a temperature sensor has lost physical contact with the internal pipework, meaning it can no longer monitor heat levels correctly.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating NTC Sensor
  • Sensor retaining clip
  • Wiring harness connector

Related codes

Full explanation for 19
Showing 21–30 of 39
20

Your boiler's internal control screen is unable to talk to the main computer, which prevents the heating from turning on.

High Engineer only £180-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal User Interface Display

Related codes

Full explanation for 20
F1

Your boiler has failed to light because it isn't receiving gas or the spark isn't igniting the fuel.

High DIY-safe £100-£350

What to check first

  1. Check that your gas prepayment meter has credit (if applicable).
  2. Ensure your gas stopcock and other gas appliances like hobs are working.
  3. Press the Reset button (indicated by a flame with a cross through it) on the boiler control panel.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F1
F2

Your boiler has stopped working because the fan that removes waste gases is not spinning correctly or has lost power.

High Engineer only £180-350

Parts commonly replaced

  • Fan motor
  • Main PCB (Printed Circuit Board)
  • Wiring harness

Related codes

Full explanation for F2
F3

Your boiler has detected a problem with how air and waste gases are moving through the system, causing it to shut down for safety.

High Engineer only £100-280

Parts commonly replaced

  • Air pressure switch
  • Venturi tube
  • Fan assembly

Related codes

Full explanation for F3
F4

Your boiler has tried to light several times but cannot establish a flame, meaning you will have no heating or hot water until it is fixed.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances, like a hob, are working to confirm your gas supply is active.
  2. If you have a pre-payment meter, check that you have enough credit.
  3. Check that your external condensate pipe hasn't frozen if it is very cold outside.
  4. Try resetting the boiler by pressing the 'Reset' button (the flame symbol with a cross).

Parts commonly replaced

  • Ignition electrodes
  • Gas valve
  • Printed Circuit Board (PCB)
  • Ignition lead

Related codes

Full explanation for F4
F5

Your boiler has shut down because its internal temperature has risen too high, usually due to a lack of water flow or a circulation blockage.

High DIY-safe £120-350

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the gauge; top up if low.
  2. Ensure all radiator valves and isolation valves under the boiler are fully open.
  3. Wait 30 minutes for the unit to cool down, then press the reset button (usually marked with a flame or 'reset').

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • NTC Temperature Sensor

Related codes

Full explanation for F5
F6

Your boiler has stopped working because a sensor that monitors the temperature of the water leaving the unit has failed or has a loose connection.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC thermistor
  • Wiring harness

Related codes

Full explanation for F6
F7

Your boiler's hot water sensor has failed or disconnected, meaning the system can no longer tell how hot the water is.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC thermistor
  • Wiring harness/sensor clip

Related codes

Full explanation for F7
F8

Your boiler has detected a sensor problem with the small internal tank used to provide instant hot water, which may cause your hot water to stay cold or be inconsistent.

Medium Engineer only £95-£160

Parts commonly replaced

  • Micro-accumulation NTC sensor
  • Wiring harness

Related codes

Full explanation for F8
F9

Your boiler has stopped working because it cannot correctly detect the water pressure, which is usually caused by a faulty internal sensor rather than a leak.

High Engineer only £120-190

Parts commonly replaced

  • Water pressure sensor
  • Circulation pump (if blocked)
  • Wiring harness

Related codes

Full explanation for F9
Showing 31–39 of 39
F11

Your boiler's internal computer has developed a fault and is unable to send the correct signals to start the heating process.

High Engineer only £280-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness

Related codes

Full explanation for F11
F13

Your boiler's main internal computer has developed a technical hardware fault and is unable to control the system.

High Engineer only £280-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring harness connectors

Related codes

Full explanation for F13
F14

Your boiler has detected a problem with how it receives its gas supply, which prevents it from lighting safely.

High Engineer only £250-£450

Parts commonly replaced

  • Gas Valve
  • Ignition Lead
  • Main PCB

Related codes

Full explanation for F14
F15

Your boiler has developed a problem with a motor that controls the gas flow, meaning it cannot ignite safely to provide heat or hot water.

High Engineer only £140-£260

Parts commonly replaced

  • Gas valve stepper motor
  • Gas valve assembly
  • Main PCB

Related codes

Full explanation for F15
F16

Your boiler is failing to detect a flame when it tries to fire up, so it has shut down for safety.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for F16
F17

Your boiler is not receiving the correct voltage of electricity, causing it to shut down to protect its internal parts.

High Engineer only £100-£350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Electrical wiring harness
  • External voltage regulator

Related codes

Full explanation for F17
F19

Your boiler has detected that a temperature sensor has come loose from its pipe, preventing it from reading the system's heat correctly.

High Engineer only £90-160

Parts commonly replaced

  • Flow/Return NTC Thermistor
  • Sensor Retaining Clip

Related codes

Full explanation for F19
F20

Your boiler's internal electronic components are having trouble communicating with each other because the control boards are not compatible or correctly configured.

High Engineer only £180-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display Interface Board

Related codes

Full explanation for F20
F21

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually two silver braided hoses) beneath the boiler.
  2. Gradually open the small black taps until you hear water entering the system.
  3. Watch the pressure gauge and close the taps once the needle reaches 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for F21