Glow-worm 30cxi Fault codes & diagnostics

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

Combi Natural Gas 30 kW 2006-2010 Discontinued

Replaced by: Flexicom cx

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43 High 1 Medium
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 44 documented codes

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All Boilers

Your boiler is not receiving enough gas or is struggling to light the flame properly.

High DIY-safe £120-350

What to check first

  1. Check that your gas meter has credit and the emergency control valve is open
  2. Search for other gas appliances in your home, like a hob, to see if they are working
  3. Press the 'Reset' button (marked with a flame or 'R') on the boiler control panel

Parts commonly replaced

  • Gas Valve
  • Ignition Electrode
  • Spark Generator
  • PCB
Full explanation for All Boilers
All Ultracom

Your boiler has lost power or has a serious internal communication error, meaning it cannot operate or tell you what is wrong.

High DIY-safe £180-£450

What to check first

  1. Check if the main boiler power switch or fused spur is turned on
  2. Check your home's consumer unit (fuse box) to see if a circuit breaker has tripped
  3. Ensure the power cable leading into the bottom of the boiler is securely connected

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Display Interface
  • Internal Fuse
Full explanation for All Ultracom
Betacom

Your boiler has detected a general operational error or a loss of flame, causing it to stop providing heating and hot water.

High DIY-safe £100-280

What to check first

  1. Check if your gas prepay meter has credit
  2. Check if other gas appliances in the house are working
  3. Press and hold 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)
Full explanation for Betacom
Betacom c

Your boiler has likely lost water pressure or there is a blockage preventing water from circulating properly, causing the system to stop heating.

High DIY-safe £80-250

What to check first

  1. Check the pressure gauge on the front of the boiler; if it is below 1.0 bar, you need to top it up.
  2. Locate the filling loop underneath the boiler and slowly turn the valves until the pressure reaches 1.5 bar.
  3. Ensure all radiator valves are open and that your pump is running if accessible.

Parts commonly replaced

  • Circulation Pump
  • Flow/Return Thermistor
  • Filling Loop Valve
Full explanation for Betacom c
Boiler Model

Your boiler has stopped working because it cannot detect a flame, meaning it has safely shut down to prevent issues.

High DIY-safe £120-£350

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas is reaching the property.
  2. Ensure your credit is topped up if you have a prepaid gas meter.
  3. Gently press the 'Reset' button (marked with a flame or cross symbol) and hold for 2 seconds.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Ignition Lead
  • PCB
Full explanation for Boiler Model
ci range

Your boiler has detected an internal fault with its control board or electronic circuit, meaning it cannot operate safely and has shut down.

High Engineer only £220-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness
Full explanation for ci range
Compact e / s

Your boiler is providing central heating as normal but is failing to produce any hot water when you turn on your taps.

Medium Engineer only £140-£260

Parts commonly replaced

  • Diverter Valve
  • DHW Plate Heat Exchanger
  • DHW Flow Sensor
Full explanation for Compact e / s
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.00

Your boiler has stopped working because it cannot accurately measure the temperature of the water leaving the unit.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature sensor (NTC thermistor)
  • Sensor wiring harness

Related codes

Full explanation for F.00
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
Showing 11–20 of 44
F.11

Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water leaving the unit, preventing it from heating up safely.

High Engineer only £100-180

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring harness / sensor lead

Related codes

Full explanation for F.11
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.20

Your boiler has shut down because its internal temperature has gotten too high and it is now locked out for safety.

High DIY-safe £100-350

What to check first

  1. Check all radiator valves are open and not turned to zero
  2. Ensure the system pressure is between 1.0 and 1.5 bar on the gauge
  3. Press the 'Reset' button (represented by a flame with a cross through it) once to restart the boiler

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • NTC Temperature Sensor

Related codes

Full explanation for F.20
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.23

Your boiler has shut down because the water inside is heating up too quickly or unevenly, usually due to a circulation problem.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Bleed any air from your radiators

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensors
  • Heat Exchanger (Cleaning/Replacement)

Related codes

Full explanation for F.23
F.24

Your boiler has shut down because it is heating up much faster than it should, usually because the water isn't moving through the system properly.

High DIY-safe £120-300

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar on the clear display
  3. Try resetting the boiler to see if the fault clears

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger (flushing/cleaning)
  • Thermistor

Related codes

Full explanation for F.24
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.27

Your boiler has shut down because it thinks a flame is present even when it should be off, or it cannot correctly sense the flame it has lit.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for F.27
F.28

Your boiler has tried to light itself three times but failed to stay on, meaning you currently have no heating or hot water.

High DIY-safe £100-350

What to check first

  1. Check if your gas meter has credit (if on a prepayment meter)
  2. Verify that other gas appliances in your home, like a hob, are working correctly
  3. Check if your external condensate pipe is frozen during cold weather
  4. Press the Reset button (the flame symbol with a cross) for one second

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Leads

Related codes

Full explanation for F.28
F.29

Your boiler has lost its flame while it was running and cannot restart, which means your heating and hot water have stopped working.

High DIY-safe £120-350

What to check first

  1. Press the reset button (indicated by a flame with a line through it) for five seconds.
  2. Check that your gas pre-payment meter hasn't run out of credit.
  3. Check that other gas appliances in your home, like a hob, are still working.
  4. In freezing weather, check if the white plastic pipe leading outside is frozen and thaw it with warm water.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sense Electrode
  • Spark Generator

Related codes

Full explanation for F.29
Showing 21–30 of 44
F.32

Your boiler's fan is running at the wrong speed to prevent freezing or is struggling to startup correctly in cold conditions.

High Engineer only £180-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for F.32
F.33

Your boiler has paused because it cannot confirm the fan is working correctly, often due to extremely cold weather or a blocked air pipe.

High Engineer only £90-180

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Venturi tube

Related codes

Full explanation for F.33
F.61

Your boiler has detected a communication problem with the gas valve, meaning it cannot safely ignite to provide heating or hot water.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB
  • Gas Valve
  • Wiring Harness

Related codes

Full explanation for F.61
F.64

Your boiler's internal computer is struggling to process signals from its sensors, causing the system to shut down for safety.

High Engineer only £180-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • NTC Thermistor Sensors
  • Wiring Loom

Related codes

Full explanation for F.64
F.67

Your boiler's electronic control board is receiving a confusing signal regarding the flame, which has caused the system to shut down for safety.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Ignition Electrode
  • Wiring Harness

Related codes

Full explanation for F.67
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.71

Your boiler has detected that the sensors responsible for measuring water temperature are giving conflicting or incorrect readings, causing the system to shut down for safety.

High Engineer only £90-180

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness

Related codes

Full explanation for F.71
F.72

Your boiler has detected that two internal sensors are disagreeing with each other, which usually means one of them is faulty or incorrectly fitted.

High Engineer only £120-190

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • Water pressure sensor

Related codes

Full explanation for F.72
F.73

Your boiler has lost communication with its water pressure sensor, meaning it cannot confirm there is enough water inside to operate safely.

High Engineer only £140-£260

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for F.73
F.74

Your boiler has detected an electrical fault with the sensor that monitors water pressure, preventing it from heating your home safely.

High Engineer only £120-£200

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

Full explanation for F.74
Showing 31–40 of 44
F.75

Your boiler has detected that the water pump is running but cannot sense the required change in pressure to safely start the heating process.

High DIY-safe £130-£250

What to check first

  1. Check the pressure gauge on the front of the boiler is between 1.0 and 1.5 bar
  2. If pressure is low, use the filling loop to top up the water level
  3. Reset the boiler using the flame symbol button to see if the fault clears

Parts commonly replaced

  • Water pressure sensor
  • Circulation pump
  • Expansion vessel

Related codes

Full explanation for F.75
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
F.78

Your boiler has shut down because a specific safety sensor inside the main heating unit has stopped working correctly.

High Engineer only £120-£250

Parts commonly replaced

  • Overheat thermostat
  • Primary heat exchanger sensor
  • Wiring harness

Related codes

Full explanation for F.78
F.82

Your boiler has detected a safety issue with the gas flow connection, meaning it cannot light correctly and has shut down for protection.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for F.82
F.83

Your boiler's computer brain has suffered a data memory error and can no longer communicate with the rest of the unit.

High Engineer only £250-£400

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Interface Board

Related codes

Full explanation for F.83
F.84

Your boiler is confused because its internal temperature sensors are giving conflicting readings, causing it to shut down for safety.

High Engineer only £100-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor Wiring Harness
  • Main PCB

Related codes

Full explanation for F.84
F.85

Your boiler's internal computer has become too hot and has shut itself down to prevent damage to the circuitry.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • NTC Temperature Sensor

Related codes

Full explanation for F.85
F.87

Your boiler is having trouble creating the spark needed to light the gas or cannot properly detect that a flame is present.

High Engineer only £120-£240

Parts commonly replaced

  • Ignition Electrodes
  • Ignition Lead
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F.87
F.88

Your boiler is struggling to keep a steady flame lit, which is causing it to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

  • Gas Valve
  • Flame Sensing Electrode
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F.88
F.89

Your boiler has stopped working because the pump that moves hot water around your heating system has developed a fault or is stuck.

High Engineer only £220-£380

Parts commonly replaced

  • Circulating Pump
  • Pump head
  • Main PCB

Related codes

Full explanation for F.89
Showing 41–44 of 44
FA9

Your boiler's internal communication system has lost power, meaning the different parts of the unit cannot talk to each other to start the heating process.

High Engineer only £150-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal Wiring Loom
  • External Control Interface
Full explanation for FA9
hxi range

Your boiler has detected an issue circulating water or a sensor failure, which has caused it to stop working to protect itself.

High Engineer only £120-£350

Parts commonly replaced

  • Pressure Sensor
  • Circulation Pump
  • Printed Circuit Board (PCB)
Full explanation for hxi range
Ultracom₂ 35 Store

Your boiler has likely detected a problem with the temperature sensors or its internal memory, preventing it from heating your water correctly.

High Engineer only £120-£350

Parts commonly replaced

  • NTC Temperature Sensor
  • Printed Circuit Board (PCB)
  • Wiring Harness
Full explanation for Ultracom₂ 35 Store
Xtramax HE Range

Your boiler is overheating because the water is not flowing through the system quickly enough or the temperature is rising too fast.

High DIY-safe £150-£400

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar on the gauge
  2. Ensure all radiator valves are fully open to allow water flow
  3. Try resetting the boiler using the flame/reset button

Parts commonly replaced

  • Central heating pump
  • Primary heat exchanger
  • NTC temperature sensors
Full explanation for Xtramax HE Range