Glow-worm 30cxi Fault codes & diagnostics

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

Combi Natural Gas 30 kW 2007-2013 Discontinued
GC Number 47-019-02

Replaced by: Flexicom cx

Download the Glow-worm 30cxi manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
8 High
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
47-019-02 Ultracom 30cxi 2007–2013
Just want the most common Glow-worm 30cxi 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

Connection

Your boiler's internal control screen is unable to talk to the main computer brain, meaning it cannot receive the instructions needed to heat your home.

High Engineer only £180-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • User Interface Unit
  • Internal Wiring Harness
Full explanation for Connection
F.10

Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water flowing to your radiators.

High Engineer only £90-160

Parts commonly replaced

  • NTC Flow Sensor
  • Wiring harness connector

Related codes

Full explanation for F.10
F.13

Your boiler has detected a wiring or sensor fault with the hot water supply, meaning it cannot safely monitor the temperature of your water.

High Engineer only £90-160

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor Wiring Harness
Full explanation for F.13
F.22

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 (usually two blue levers or a flexible silver hose) under the boiler.
  2. Open the valves slowly until you hear water entering and see the pressure gauge rise.
  3. Close both valves firmly when the gauge reaches 1.5 bar, then restart the boiler if necessary.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F.22
F.25

Your boiler has shut down because the exhaust fumes are getting too hot, which is a safety measure to prevent damage to the internal components.

High Engineer only £150-£450

Parts commonly replaced

  • Heat exchanger
  • Flue gas NTC sensor
  • Primary heat exchanger cleaning kit

Related codes

Full explanation for F.25
F.43

Your boiler is experiencing an internal communication fault between its main components, which has caused it to shut down for safety.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for F.43
F.70

Your boiler's computer memory has been lost or corrupted, meaning the main control board no longer knows which model of boiler it is supposed to be operating.

High Engineer only £100-£350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Display Interface

Related codes

Full explanation for F.70
F.77

Your boiler has detected a blockage in the drainage pipe or the flue, preventing waste liquids or gases from escaping properly.

High DIY-safe £90-250

What to check first

  1. Check the white plastic pipe leading outside to see if it is frozen or blocked.
  2. If frozen, gently pour warm (not boiling) water over the external pipe to thaw it.
  3. Clear any debris, such as leaves or nests, from around the flue terminal on your outside wall.

Parts commonly replaced

  • Condensate trap
  • Condensate pump
  • Flue pressure switch

Related codes

Full explanation for F.77
Status & diagnostic codes

39 operating states & engineer diagnostics

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

d.91 Diagnostic Your boiler is currently performing a routine automated background check or internal data update, which is a normal part of its scheduled operation. d.92 Diagnostic Your boiler's internal timer settings are currently being adjusted or are in a configuration mode, which is a normal status message rather than a breakdown. S.00 Status Your boiler is currently in standby mode because it has reached the temperature set on your thermostat and is not currently being asked to provide heat or hot water. S.01 Status Your boiler is currently performing a standard safety check of its ventilation fan before igniting the flame. S.02 Status Your boiler is currently preparing itself by circulating water before it attempts to light the burner. S.03 Status Your boiler is failing to light the burner, meaning it cannot produce heat or hot water. S.04 Status Your boiler is working exactly as it should and is currently heating your home. S.05 Status Your boiler is currently running its cooling cycle to move excess heat away from the system, which is a normal part of its operation. S.06 Status Your boiler is currently running its fan to clear out any leftover gases after a heating cycle, which is a normal part of the shutdown process. S.07 Status Your boiler is currently cooling itself down after use and is operating exactly as it should to protect its internal components. S.08 Status Your boiler is taking a short, programmed rest to prevent it from switching on and off too frequently. S.10 Status Your boiler is simply indicating that it has received a request to provide hot water to your taps or shower. S.11 Status Your boiler is currently checking its internal ventilation system before it starts the ignition process. S.13 Status Your boiler is failing to start because it cannot detect a flame after trying to ignite. S.14 Status Your boiler is operating normally and is currently heating water for your taps or shower. S.15 Status Your boiler is currently running its internal pump or fan longer than expected to safely clear out heat or gases, which is usually a normal part of the cooling down process. S.16 Status Your boiler is continuing to run its internal fan after the heating or hot water has switched off to clear out any leftover gases. S.17 Status Your boiler is currently running its internal pump to safely circulate leftover heat, which is a normal part of the cooling-down process. S.20 Status Your boiler is currently working correctly to provide hot water, and this code is simply a status message confirming it is in the process of heating your water. S.21 Status Your boiler is currently performing a standard safety check of its internal ventilation fan before it attempts to light the burner. S.22 Status Your boiler is currently preparing the internal water pump to circulate heat, which is a normal part of the start-up sequence. S.23 Status Your boiler is failing to light the flame properly, which means it cannot produce heating or hot water for your home. S.24 Status Your boiler is working perfectly and is currently heating up a small amount of water to ensure you get hot water at your taps more quickly. S.25 Status Your boiler is struggling to circulate water properly after the burners have turned off, which can lead to it overheating. S.26 Status Your boiler is currently running its fan to clear out any leftover gases after a cycle, which is a normal part of the shutdown process. S.27 Status Your boiler is currently running its internal pump to move remaining heat away from the burner, which is a normal part of the cooling-down process. S.28 Status Your boiler is currently taking a temporary, automatic rest period to prevent it from switching on and off too frequently. S.30 Status Your boiler is currently idle because it is not receiving a signal from your thermostat or timer to turn the heating on. S.31 Status Your boiler is currently set to summer mode, which means it will only provide hot water to your taps and will not switch on your central heating radiators. S.32 Status Your boiler is temporarily pausing its operation to protect itself from freezing while it adjusts its internal fan settings. S.34 Status Your boiler has automatically switched on its internal heating to prevent its pipes from freezing during cold weather. S.36 Status Your boiler is currently idle because it is not receiving a signal from your thermostat or timer to turn on the heating. S.42 Status Your boiler has detected a communication error with an external add-on control, such as an internet gateway or smart thermostat controller, which is preventing the boiler from firing up. S.53 Status Your boiler has detected that the water inside is not circulating properly between the heating pipes, so it is pausing briefly to let the temperature even out. S.54 Status Your boiler has detected that there is not enough water circulating inside the system or that the water is heating up far too quickly, so it has paused itself to prevent damage. S.76 Status Your boiler is momentarily pausing its operation while it double-checks the water pressure levels inside the system to ensure it is safe to fire up. S.96 Status Your boiler is currently performing a routine internal safety check on its water temperature sensors and will resume normal operation once this process completes. S.97 Status Your boiler is currently performing a routine internal safety check on its water levels and has temporarily paused your heating and hot water to ensure it is safe to operate. S.98 Status Your boiler is currently performing a routine internal safety self-check, which is temporarily pausing your hot water and heating while it verifies its internal temperature readings.