Glow-worm Ci Plus Fault codes & diagnostics

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

CombiSystem Natural Gas 24-30 kW 2001-2003 Discontinued
GC Numbers 41-047-7047-047-2847-047-21

Replaced by: Flexicom

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

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.
18 High 1 Medium
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
47-047-21 24ci Plus 2001–2003
Just want the most common Glow-worm Ci Plus faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 19 documented codes

Tap any card for details

0.5bar

Your boiler has stopped working because the water pressure has dropped too low to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (the flexible silver hose) underneath or near the boiler.
  2. Slowly open the one or two small taps on the hose until you hear water flowing.
  3. Watch the pressure gauge and close the taps firmly when the needle reaches 1.5 bar.

Parts commonly replaced

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

Your boiler has tried to ignite but failed, likely because gas isn't reaching the burner or the flame isn't being detected.

High DIY-safe £90-280

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 pre-payment meter, ensure you have sufficient credit available.
  3. Press the 'Reset' button (often indicated by a flame with a cross through it) to see if the boiler restarts.

Parts commonly replaced

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

Related codes

Full explanation for 01
02

Your boiler has stopped working because it cannot safely vent waste gases or confirm that the internal fan is running correctly.

High Engineer only £120-280

Parts commonly replaced

  • Fan
  • Air Pressure Switch
  • PCB

Related codes

Full explanation for 02
2.7bar

Your boiler has too much water inside it, which has caused the pressure to rise to a level where the system may shut down or leak to protect itself.

Medium DIY-safe £0-120

What to check first

  1. Check that the filling loop valves are fully closed
  2. Bleed water from a radiator using a bleed key to reduce pressure
  3. Monitor the pressure gauge until it returns to between 1.0 and 1.5 bar
  4. Once pressure is lowered, press the reset button

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve
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 £100-£350

What to check first

  1. Turn the boiler off and allow it to cool for 20 minutes
  2. Check that your radiator valves are open and not turned to zero
  3. Press the reset button (usually marked with a flame or 'reset' symbol) to restart the unit

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Heat Exchanger

Related codes

Full explanation for 05
06

Your boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit to heat your radiators.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Flow NTC Thermistor
  • Wiring harness connector

Related codes

Full explanation for 06
09

Your boiler has lost track of the system's water pressure because the internal sensor is failing or disconnected, causing the unit to shut down for safety.

High Engineer only £140-£220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

Full explanation for 09
11

Your boiler's display panel has lost its connection to the main computer inside, meaning the system cannot receive instructions or show you what is going wrong.

High Engineer only £120-250

Parts commonly replaced

  • MMI communication lead
  • User interface display panel
  • Main PCB

Related codes

Full explanation for 11
12

Your boiler is having trouble communicating with its control screen or your thermostat, which is preventing it from receiving your heating instructions.

High Engineer only £120-£350

Parts commonly replaced

  • User Interface PCB
  • Main Control Board
  • Wiring Harness

Related codes

Full explanation for 12
13

Your boiler's internal computer has encountered a critical error and can no longer communicate with the rest of the system.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 13
14

Your boiler has shut down because the water inside it has become too hot, triggered by a safety sensor to prevent damage.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves are open and not turned to zero.
  2. Ensure there is enough water pressure by checking the gauge is between 1 and 1.5 bar.
  3. Wait 15 minutes for the unit to cool down and try pressing the reset button.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • Main Heat Exchanger (descaling)
Full explanation for 14
15

Your boiler is unable to control the flow of gas correctly to create a flame, meaning your heating and hot water will not work.

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 an issue with the internal valve that controls the flow of gas, causing the system to shut down for safety purposes.

High Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 16
17

Your boiler is not receiving enough electrical power from your home's mains supply to operate safely.

High Engineer only £100-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Mains voltage regulator

Related codes

Full explanation for 17
18

Your boiler's main control panel has lost communication with the internal system, meaning your settings or commands aren't being processed correctly.

High Engineer only £180-350

Parts commonly replaced

  • User Interface (Display PCB)
  • Main Control PCB
  • Wiring harness
Full explanation for 18
19

Your boiler has stopped working because a sensor that monitors the temperature of the water in your heating system has become loose or disconnected from its pipe.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating (CH) Flow NTC Sensor
  • Wiring Harness

Related codes

Full explanation for 19
20

Your boiler's main control panel is failing to communicate with the internal system because they are not compatible or there is a software mismatch.

High Engineer only £180-350

Parts commonly replaced

  • User Interface PCB
  • Main Circuit Board (PCB)
Full explanation for 20
F1

Your boiler is failing to detect a flame after it tries to start, meaning your heating and hot water will not work.

High DIY-safe £120-300

What to check first

  1. Check that your gas meter is turned on and you have credit if using a pre-payment meter
  2. Check if other gas appliances, like a cooker, are working to confirm gas supply
  3. Press the 'Reset' button (marked with a flame or 'R') on the boiler control panel

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve
  • Ignition lead

Related codes

Full explanation for F1
F4

Your boiler is successfully igniting, but it cannot detect the flame and shuts down immediately for safety.

High Engineer only £120-280

Parts commonly replaced

  • Flame sensing electrode (Ionisation probe)
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F4