Glow-worm 38cxi Fault codes & diagnostics

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

Combi Natural Gas 38 kW 2005-2010 Discontinued

Replaced by: Flexicom cx

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Severity at a glance

Each cell = one fault code. Hover to identify.
43 High 1 Medium
Just want the most common Glow-worm 38cxi faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 44 documented codes

Tap any card for details

All Boilers

Your boiler has failed to ignite and cannot produce heat or hot water, usually because the gas supply is blocked or the ignition spark is failing.

High DIY-safe £100-£350

What to check first

  1. Check if your gas meter has credit and the isolation valve is open
  2. Check if other gas appliances, like a hob, are working correctly
  3. Try thawing the condensate pipe with warm water if it is frozen outside
  4. Press the Reset button (indicated by a flame symbol with a cross)

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
  • Spark Lead
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 your home's main electrical consumer unit has tripped
  2. Ensure the fused spur switch next to the boiler is turned on
  3. Check if any other appliances on the same circuit are working

Parts commonly replaced

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

Your boiler has likely lost flame or suffered a lockout, meaning it has shut down for safety and cannot provide heating or hot water until reset.

High DIY-safe £100-280

What to check first

  1. Locate the reset button (usually indicated by a flame with a cross through it or the power button).
  2. Press and hold the reset button for five seconds.
  3. Ensure your gas supply is active and that your prepaid meter (if applicable) has credit.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
Full explanation for Betacom
Betacom c

Your boiler has detected low water pressure in the central heating system, which is preventing it from firing up.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (a flexible silver hose) underneath your boiler.
  2. Open the small taps on either end of the hose to let water into the boiler.
  3. Close the taps once the pressure gauge on the front of the boiler reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel recharge
Full explanation for Betacom c
Boiler Model

Your boiler has likely lost power or the electronic control board is failing to communicate with the display.

High DIY-safe £150-320

What to check first

  1. Check that 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 has tripped
  3. Switch the power off for 30 seconds and then back on to attempt a reset

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Display Interface
  • Internal Fuse
Full explanation for Boiler Model
ci range

Your boiler's fan is not running at the correct speed or has failed completely, preventing the unit from starting up safely.

High Engineer only £240-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for ci range
Compact e / s

Your boiler is providing central heating but is failing to heat your water when you turn on a tap.

High Engineer only £140-£260

Parts commonly replaced

  • Diverter valve
  • Diverter valve motor/actuator
  • DHW plate heat exchanger
  • DHW flow sensor
Full explanation for Compact e / s
Connection

Your boiler's main internal computer has lost touch with the display panel on the front, meaning you cannot control your heating or hot water.

High Engineer only £180-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • User Interface Display Board
  • Internal Ribbon Cable
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 NTC Temperature 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, causing the system to shut down for safety.

High Engineer only £100-£180

Parts commonly replaced

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

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 how hot the water is as it leaves the unit, causing the system to shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • NTC Flow Sensor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for F.11
F.13

Your boiler's hot water sensor has developed an electrical fault, meaning it can no longer accurately monitor the temperature of the water in your cylinder.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW cylinder NTC sensor
  • Sensor wiring harness
Full explanation for F.13
F.20

Your boiler has switched itself off because it has become too hot inside, usually because water isn't moving through the system correctly.

High DIY-safe £100-£350

What to check first

  1. Check that your radiator valves are open to allow water to flow.
  2. Ensure the system pressure is between 1.0 and 1.5 bar on the display.
  3. Gently press the reset button (indicated by a flame with a cross through it) to restart the boiler.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger

Related codes

Full explanation for F.20
F.22

Your boiler has stopped working because there is not enough water pressure in the system 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) underneath the boiler.
  2. Open the taps slowly until you hear water entering the system.
  3. Watch the pressure gauge and close the taps once the needle reaches 1.5 bar.
  4. Reset the boiler using the flame symbol or power button.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

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 Engineer only £120-£350

Parts commonly replaced

  • Pump
  • NTC Thermistor
  • Heat Exchanger

Related codes

Full explanation for F.23
F.24

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

High DIY-safe £150-350

What to check first

  1. Check that all radiator valves are fully open to allow water to flow.
  2. Inspect the boiler pressure gauge and top it up to 1.5 bar if it is too low.
  3. Gently bleed your radiators to remove any trapped air pockets.
  4. Reset the boiler by pressing the reset button for five seconds.

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • NTC Temperature Sensors

Related codes

Full explanation for F.24
F.25

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

High Engineer only £120-350

Parts commonly replaced

  • Heat Exchanger (de-scaling)
  • Flue Gas NTC Sensor
  • Burner Seals

Related codes

Full explanation for F.25
F.27

Your boiler has shut down because it thinks it detected a flame when there shouldn't be one, or the flame signal is giving an incorrect reading.

High Engineer only £120-£350

Parts commonly replaced

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

Related codes

Full explanation for F.27
F.28

Your boiler is trying to light itself to provide heat or hot water but is failing to create a flame.

High DIY-safe £100-350

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your gas meter
  2. Test if other gas appliances in your home, 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
  • Spark Generator
  • PCB

Related codes

Full explanation for F.28
F.29

Your boiler was working but the flame has gone out unexpectedly, often because it is struggling to get enough gas or the burner is dirty.

High DIY-safe £100-£350

What to check first

  1. Check that your gas meter has credit (if on prepay) and that other gas appliances like your hob are working.
  2. Inspect the white plastic condensate pipe outside for signs of freezing or blockages.
  3. Reset the boiler by pressing the reset button (flame symbol with a cross) to see if it clears the fault.

Parts commonly replaced

  • Gas Valve
  • Ignition Lead
  • Spark Electrode
  • Condensate Trap

Related codes

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

Your boiler has detected that the fan is spinning at the wrong speed, likely due to a build-up of ice, debris, or a communication error between components.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring loom

Related codes

Full explanation for F.32
F.33

Your boiler has stopped working because the fan is unable to clear air from the system or a sensor has detected an issue with the air pressure.

High Engineer only £120-280

Parts commonly replaced

  • Air Pressure Switch
  • Fan Assembly
  • Venting/Flue Seals
Full explanation for F.33
F.61

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

High Engineer only £250-£550

Parts commonly replaced

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

Related codes

Full explanation for F.61
F.64

Your boiler's computer is having trouble processing information from its internal sensors, causing the system to shut down for safety.

High Engineer only £250-£550

Parts commonly replaced

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

Related codes

Full explanation for F.64
F.67

Your boiler has detected an internal electronics error related to the flame detection system, preventing it from firing up safely.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Ignition Electrode

Related codes

Full explanation for F.67
F.70

Your boiler's computer memory has been wiped or is mismatched, meaning it no longer recognizes which model it is supposed to be.

High Engineer only £100-£350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • User Interface/Display PCB

Related codes

Full explanation for F.70
F.71

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

High Engineer only £100-180

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 the temperature sensors on the flow and return pipes are giving conflicting readings, which prevents it from heating safely.

High Engineer only £120-£240

Parts commonly replaced

  • NTC Temperature Sensor
  • Water Pressure Sensor
  • Wiring Harness

Related codes

Full explanation for F.72
F.73

Your boiler's internal sensor that monitors water levels is unable to send a reading to the control board, preventing the system from running safely.

High Engineer only £140-£220

Parts commonly replaced

  • Digital water pressure sensor
  • Wiring harness

Related codes

Full explanation for F.73
F.74

Your boiler's internal sensor is struggling to communicate the current water pressure, which prevents the system from running safely.

High Engineer only £130-220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main PCB

Related codes

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

Your boiler is struggling to detect a rise in water pressure when the pump starts up, preventing it from firing for your heating or hot water.

High DIY-safe £140-£250

What to check first

  1. Check the pressure gauge on the front of the boiler
  2. If the pressure is below 1.0 bar, use the filling loop to top it up to 1.5 bar
  3. Press the reset button (indicated by a flame with a cross through it) to restart the boiler

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 system or an issue with the flue, causing it to shut down to prevent water or exhaust gases from backing up.

High DIY-safe £90-180

What to check first

  1. Check the white plastic pipe under the boiler for any obvious kinks or blockages.
  2. If the weather is freezing, check the external condensate pipe for ice and gently pour warm (not boiling) water over it to thaw.
  3. Inspect the external flue terminal for any visible obstructions like leaves or bird nests.

Parts commonly replaced

  • Condensate trap
  • Condensate pump (if fitted)
  • Flue pressure switch

Related codes

Full explanation for F.77
F.78

Your boiler has shut down because a built-in safety sensor has detected a fault within the main heating component.

High Engineer only £140-£280

Parts commonly replaced

  • Primary heat exchanger safety sensor
  • Overheat thermostat
  • Wiring harness

Related codes

Full explanation for F.78
F.82

Your boiler has detected a safety issue with the gas valve and has shut down to prevent an unsafe burner flame.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F.82
F.83

Your boiler's computer brain has suffered a memory error and can no longer process the instructions needed to run properly.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display Interface

Related codes

Full explanation for F.83
F.84

Your boiler is confused because its temperature sensors are giving contradictory readings, preventing it from heating up safely.

High Engineer only £120-£200

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness

Related codes

Full explanation for F.84
F.85

Your boiler's internal computer is overheating, causing the system to shut down to prevent damage.

High Engineer only £180-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal Wire Harness

Related codes

Full explanation for F.85
F.87

Your boiler is having trouble creating the spark needed to light the gas burner and has shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Ignition electrodes
  • Ionisation probe
  • Ignition lead
  • Gas valve

Related codes

Full explanation for F.87
F.88

Your boiler is struggling to maintain a steady flame or is detecting an issue with its safety controls, causing the system to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

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

Related codes

Full explanation for F.88
F.89

Your boiler has stopped working because the internal pump is unable to circulate water throughout the system.

High Engineer only £250-450

Parts commonly replaced

  • Circulation Pump
  • Connection Cable
  • Main PCB

Related codes

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

Your boiler is having trouble communicating with its internal controls or external thermostat due to an electrical connection issue.

High Engineer only £100-£350

Parts commonly replaced

  • Main PCB
  • eBUS wiring harness
  • External thermostat/controller
Full explanation for FA9
hxi range

Your boiler has detected an issue with the water pressure or the sensor that monitors it, preventing the system from heating up safely.

High DIY-safe £100-280

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1.0 and 1.5 bar.
  2. If the pressure is below 1.0 bar, use the filling loop underneath the boiler to increase it.
  3. Once the pressure is corrected, press the 'Reset' button to restart the boiler.

Parts commonly replaced

  • Water pressure sensor
  • Circulation pump
  • Expansion vessel recharge
Full explanation for hxi range
Ultracom₂ 35 Store

Your boiler has likely stopped heating because a temperature sensor is either disconnected or has developed a fault.

High Engineer only £90-180

Parts commonly replaced

  • Flow NTC Thermistor
  • Return NTC Thermistor
  • Wiring Harness
Full explanation for Ultracom₂ 35 Store
Xtramax HE Range

Your boiler has detected that the water temperature is rising too quickly, which usually means water isn't circulating properly through the system.

High Engineer only £150-£400

Parts commonly replaced

  • Pump
  • Primary Heat Exchanger
  • NTC thermistor
Full explanation for Xtramax HE Range