Glow-worm HXi Fault codes & diagnostics

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

System Natural Gas 15-24 kW 2013-2017 Discontinued

Replaced by: Energy System

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.
43 High 1 Medium
Just want the most common Glow-worm HXi 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, which is usually due to an interrupted gas supply, a blocked condensate pipe, or a component failure.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is on.
  2. If it is freezing outside, check if the white plastic condensate pipe leading outdoors is frozen and thaw it with warm water.
  3. Press the reset button (usually marked with a flame or 'reset') and hold for five seconds.

Parts commonly replaced

  • Gas valve
  • Ignition lead and electrodes
  • Printed Circuit Board (PCB)
Full explanation for All Boilers
All Ultracom

Your boiler has lost power or is experiencing a total electronics failure, meaning it cannot operate or tell you what is wrong.

High DIY-safe £150-£450

What to check first

  1. Check if your main consumer unit (fuse box) has tripped and reset it.
  2. Verify the boiler's fused spur switch is turned on and the fuse has not blown.
  3. Check if other appliances in your home have power to rule out a general power cut.

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Display Interface Board
  • Transformer
Full explanation for All Ultracom
Betacom

Your boiler has detected a fault and has locked itself out to prevent damage or unsafe operation.

High DIY-safe £120-350

What to check first

  1. Locate the reset button (usually marked with a flame or 'R' symbol) on the control panel.
  2. Press and hold the reset button for five seconds, then release.
  3. Wait 2 minutes for the boiler to restart; if the red light returns, call a Gas Safe engineer.

Parts commonly replaced

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

Your boiler has likely lost pressure or is struggling to circulate water, which has caused it to stop running for safety.

High DIY-safe £80-160

What to check first

  1. Check the pressure gauge on the boiler or under the sink; it should be between 1 and 1.5 bar.
  2. If the pressure is low, use the filling loop valves to top the system up until the needle is in the green zone.
  3. Turn the selector knob to 'Reset' for five seconds, then turn it back to the original position.

Parts commonly replaced

  • Circulation Pump
  • Expansion Vessel
  • Overheat Thermostat
Full explanation for Betacom c
Boiler Model

Your boiler has lost its internal configuration, meaning it no longer knows which model it is and has stopped working for safety.

High Engineer only £100-280

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Model Recognition Chip
Full explanation for Boiler Model
ci range

Your boiler's internal computer or memory chip has detected a communication error and needs to be reset or inspected by a professional.

High Engineer only £180-450

Parts commonly replaced

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

Your boiler is working for your heating, but it is currently unable to provide hot water to your taps or shower.

High Engineer only £180-£350

Parts commonly replaced

  • Diverter Valve
  • Flow Sensor
  • Domestic Hot Water Heat Exchanger

Related codes

Full explanation for Compact e / s
Connection

Your boiler's internal control board and the display panel have lost touch with each other, meaning the boiler cannot receive your commands to turn on.

High Engineer only £180-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • User Interface Board
  • Internal Wiring Loom

Related codes

Full explanation for Connection
F.00

Your boiler has lost connection with its internal thermometer, meaning it cannot safely tell how hot the water is and has stopped running as a precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature NTC sensor
  • Wiring harness connection

Related codes

Full explanation for F.00
F.10

Your boiler's internal thermometer has developed a fault and can no longer tell how hot the water is, causing the system to shut down for safety.

High Engineer only £100-180

Parts commonly replaced

  • Flow temperature sensor (NTC thermister)
  • Internal wiring loom

Related codes

Full explanation for F.10
Showing 11–20 of 44
F.11

Your boiler's internal thermometer has developed an electrical fault and can no longer accurately measure the temperature of the water leaving the unit, causing it to shut down for safety.

High Engineer only £90-£160

Parts commonly replaced

  • Flow temperature NTC sensor
  • Wiring harness

Related codes

Full explanation for F.11
F.13

Your boiler has detected an electrical fault with the sensor that monitors the temperature of your hot water cylinder, meaning it cannot heat your water correctly.

Medium Engineer only £90-160

Parts commonly replaced

  • NTC temperature sensor
  • Wiring harness
  • Solar/Cylinder NTC

Related codes

Full explanation for F.13
F.20

Your boiler has automatically shut down because it detected that the internal temperature has become too high, preventing it from overheating.

High DIY-safe £100-280

What to check first

  1. Check that your radiator valves are fully open to allow water to flow.
  2. Ensure there is no air trapped in the system by bleeding your radiators.
  3. Press the reset button (indicated by a flame with a cross through it) 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 inside the system has dropped too low to operate safely.

High DIY-safe £0-160

What to check first

  1. Locate the external filling loop, which is usually a flexible silver hose with small valves underneath or near the boiler.
  2. Slowly open the valve (or valves) to allow water to enter the system while watching the pressure gauge.
  3. Close the valves tightly once the pressure gauge reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for F.22
F.23

Your boiler has shut down because it detected that the water temperature is changing too quickly or unevenly, often due to a circulation problem.

High Engineer only £120-350

Parts commonly replaced

  • Circulation Pump
  • NTC Thermistor Sensors
  • Heat Exchanger (Cleaning)

Related codes

Full explanation for F.23
F.24

Your boiler has switched itself off because the water inside it is heating up too quickly, which usually means the water isn't flowing through the system properly.

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 on the gauge
  3. Try resetting the boiler to see if the fault clears

Parts commonly replaced

  • Circulation pump
  • Flow/Return thermistor
  • Main heat exchanger (cleaning)

Related codes

Full explanation for F.24
F.25

Your boiler has shut down because the internal exhaust gases are getting too hot, which is a safety feature to prevent damage to the appliance.

High Engineer only £120-350

Parts commonly replaced

  • Heat exchanger
  • Flue gas NTC sensor
  • Burner seals

Related codes

Full explanation for F.25
F.27

Your boiler has sensed a flame when there shouldn't be one, or the device that monitors the fire is faulty, causing the system to shut down for safety.

High Engineer only £100-280

Parts commonly replaced

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

Related codes

Full explanation for F.27
F.28

Your boiler is trying to start up but cannot light the gas 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. Check if other gas appliances in your home, like a hob, are working correctly
  3. Reset the boiler by pressing the reset button (flaming cylinder icon) for five seconds

Parts commonly replaced

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

Related codes

Full explanation for F.28
F.29

Your boiler was working but the flame has gone out unexpectedly, often due to a temporary interruption in the gas supply or a drainage issue.

High DIY-safe £90-250

What to check first

  1. Check that your gas meter has credit and the isolation valve is open
  2. Inspect the white plastic condensate pipe outside for signs of freezing or blockage
  3. Press the reset button (indicated by a flame symbol with a cross) on the boiler control panel

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe

Related codes

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

Your boiler has detected that the internal fan is spinning at the wrong speed, possibly due to extreme cold or a mechanical fault, and has shut down as a precaution.

High Engineer only £180-450

Parts commonly replaced

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

Related codes

Full explanation for F.32
F.33

Your boiler has stopped working because it cannot confirm the fan is running safely, often triggered by extremely cold weather or a sensor issue.

High Engineer only £120-280

Parts commonly replaced

  • Air Pressure Switch
  • Fan Assembly
  • Silicone Tubing

Related codes

Full explanation for F.33
F.61

Your boiler has detected an internal communication error between the main control board and the gas valve, preventing it from lighting safely.

High Engineer only £250-£550

Parts commonly replaced

  • Gas valve
  • Main Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for F.61
F.64

Your boiler's internal computer is having trouble processing information 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 has detected an internal communication error regarding its flame detection system, causing it to shut down for safety.

High Engineer only £180-450

Parts commonly replaced

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

Related codes

Full explanation for F.67
F.70

Your boiler's control board and display screen are struggling to talk to each other because the system's identity settings have been lost or mismatched.

High Engineer only £120-£350

Parts commonly replaced

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

Related codes

Full explanation for F.70
F.71

Your boiler is confused because its temperature sensors are giving conflicting readings, causing it 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 giving conflicting information about the water temperature or pressure, causing the system to shut down for safety.

High Engineer only £120-£250

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • Water pressure sensor
  • Wiring loom

Related codes

Full explanation for F.72
F.73

Your boiler has lost signal from the internal sensor that checks water pressure, meaning it cannot confirm if it is safe to operate.

High Engineer only £120-190

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

Full explanation for F.73
F.74

Your boiler's internal sensor that monitors water pressure has experienced an electrical failure and can no longer tell if there is enough water in the system.

High Engineer only £140-£220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

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

Your boiler is struggling to detect a rise in pressure when the pump starts, which means it cannot safely confirm that water is circulating properly.

High DIY-safe £140-£250

What to check first

  1. Check the pressure gauge on the front of the boiler or under the sink.
  2. If the pressure is below 1.0 bar, use the filling loop to top it up to 1.5 bar.
  3. Reset the boiler to see if the error clears.

Parts commonly replaced

  • Water pressure sensor
  • Circulating pump

Related codes

Full explanation for F.75
F.77

Your boiler has detected a blockage in the drainage pipe or a problem with the fan system, causing it to shut down for safety.

High DIY-safe £100-£280

What to check first

  1. Check the white plastic pipe leading outside for signs of ice or blockages.
  2. If frozen, gently pour warm (not boiling) water over the pipe to thaw it.
  3. Reset the boiler using the power button or reset switch.

Parts commonly replaced

  • Condensate trap
  • Condensate pump
  • Fan assembly

Related codes

Full explanation for F.77
F.78

Your boiler has detected a fault with a safety sensor meant to prevent the main heat exchanger from overheating, causing the system to shut down for protection.

High Engineer only £120-£250

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 valve that controls the gas supply, meaning it has shut down to prevent an incorrect amount of fuel from entering the system.

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 internal computer has suffered a memory error and can no longer process the instructions needed to run safely.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for F.83
F.84

Your boiler is getting confused by contradictory temperature readings and has switched itself off to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness

Related codes

Full explanation for F.84
F.85

Your boiler's internal control board 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 Wiring Harness

Related codes

Full explanation for F.85
F.87

Your boiler is having trouble creating or detecting the flame needed to heat your water, usually because the internal ignition components are worn or faulty.

High Engineer only £120-£220

Parts commonly replaced

  • Ignition electrode
  • Flame sensing electrode
  • 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 or there is a communication error 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
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F.88
F.89

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

High Engineer only £220-£380

Parts commonly replaced

  • Central heating pump
  • Wiring harness
  • Main PCB

Related codes

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

Your boiler is having trouble communicating internally because the electrical voltage connecting its main components has dropped too low.

High Engineer only £120-£350

Parts commonly replaced

  • Main PCB
  • eBUS cable
  • User interface module
Full explanation for FA9
hxi range

Your boiler has detected an issue with the water circulation or a faulty sensor, preventing it from heating up safely.

High Engineer only £120-£350

Parts commonly replaced

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

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

High Engineer only £90-180

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness
Full explanation for Ultracom₂ 35 Store
Xtramax HE Range

Your boiler has detected that the water temperature is rising far too quickly, often because water isn't flowing through the system as it should.

High DIY-safe £180-450

What to check first

  1. Ensure all radiator valves and lockdowns are fully open
  2. Check that the boiler pressure is between 1.0 and 1.5 bar
  3. Gently restart the boiler using the reset button

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • NTC Temperature Sensors
Full explanation for Xtramax HE Range