Glow-worm Ultracom 2 HXI Fault codes & diagnostics

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

Regular Natural Gas 12-30 kW 2007-2013 Discontinued

Replaced by: Flexicom sx

Download the Glow-worm Ultracom 2 HXI manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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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.
1 Emergency 12 High 1 Medium
Just want the most common Glow-worm Ultracom 2 HXI faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 14 documented codes

Tap any card for details

F1

Your boiler has failed to ignite and has shut itself down for safety, meaning you will not have any heating or hot water until it is reset or repaired.

High DIY-safe £100-350

What to check first

  1. Check if your gas meter has credit and other gas appliances like the hob are working
  2. Press the Reset button (indicated by a flame with a cross through it) for five seconds
  3. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  4. If it is freezing outside, check that your white plastic condensate pipe hasn't frozen

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
  • Spark Lead

Related codes

Full explanation for F1
F3

Your boiler has detected an issue with the internal air circulation system, which has caused it to stop heating as a safety precaution.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

Full explanation for F3
F4

Your boiler is struggling to keep its flame lit while it is trying to heat your home, causing it to shut down for safety.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Flame rectification sensor
  • Gas valve
  • PCB

Related codes

Full explanation for F4
F5

Your boiler has switched itself off for safety because it has reached an excessively high temperature, likely due to a circulation problem.

High DIY-safe £100-350

What to check first

  1. Check that your radiator valves are fully open and not turned down.
  2. Ensure there is enough water pressure in the system by checking the gauge.
  3. Try resetting the boiler by pressing the reset button to see if it clears the lockout.

Parts commonly replaced

  • Circulating Pump
  • Overheat Thermostat
  • Main Heat Exchanger

Related codes

Full explanation for F5
F10

Your boiler has detected a problem with the sensor that measures the temperature of the water leaving the unit, causing it to shut down as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC thermistor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for F10
F13

Your boiler's hot water sensor has developed a technical fault, preventing the system from accurately measuring and heating your water.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Thermistor (NTC Sensor)
  • Wiring harness connector
Full explanation for F13
F14

Your boiler has detected an issue with the internal component that regulates the gas supply, meaning it has safely shut down to prevent unsafe operation.

Emergency Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for F14
F15

Your boiler is having trouble communicating with its internal control system, which is preventing it from starting up or operating correctly.

High Engineer only £150-300

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Wiring harness
  • eBus connector

Related codes

Full explanation for F15
F22

Your boiler has detected that the water pressure is too low to operate safely and has shut down to prevent damage.

High DIY-safe £60-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath the boiler.
  2. Open the one or two small valves on the hose until you hear water flowing.
  3. Watch the pressure gauge and close the valves when the needle reaches 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F22
F25

Your boiler has switched itself off because the internal exhaust gases have reached a temperature that is too high, often caused by a circulation problem or a lack of water.

High DIY-safe £120-350

What to check first

  1. Check the boiler pressure gauge and top it up to 1.5 bar if it is too low
  2. Ensure all radiator valves are fully open to allow water to flow
  3. Try resetting the boiler once the system has cooled down

Parts commonly replaced

  • Primary Heat Exchanger
  • Flue NTC Sensor
  • Pump

Related codes

Full explanation for F25
F43

Your boiler has lost its memory of whether it is a 24kW or 30kW model, meaning it cannot operate safely until its settings are re-programmed.

High Engineer only £90-180

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for F43
F70

Your boiler's main control board has lost communication with its internal identity chip, effectively meaning the boiler has forgotten which model it is and cannot operate.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • DSN (Device Specific Number) Chip

Related codes

Full explanation for F70
F77

Your boiler has detected an issue with the system that removes waste water or measured a temperature imbalance, causing it to shut down as a safety precaution.

High Engineer only £120-250

Parts commonly replaced

  • Condensate pump
  • Flue gas thermistor
  • Wiring harness

Related codes

Full explanation for F77
F141

Your boiler is unable to read the temperature of the water flowing through it because one of its sensors is sending an incorrect or missing signal.

High Engineer only £120-220

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness

Related codes

Full explanation for F141
Status & diagnostic codes

37 operating states & engineer diagnostics

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

S.00 Status Your boiler is working correctly and is currently in standby mode because your thermostat has reached the desired temperature or the heating timer is off. S.01 Status Your boiler is preparing to start the heating process by running the internal fan to clear out the combustion chamber. S.02 Status Your boiler is performing a routine start-up check by running the internal pump for a few moments before lighting the burner. S.03 Status Your boiler is currently attempting to light the flame but is failing to do so, meaning you won't have heating or hot water until it succeeds. S.04 Status Your boiler is working normally and is currently firing up to provide hot water for your taps or showers. S.05 Status Your boiler is temporarily cooling itself down after finishing a heating or hot water cycle, which is a normal part of its operation. S.06 Status Your boiler's fan is continuing to run after it should have stopped, causing the system to pause for safety reasons. S.07 Status Your boiler is continuing to run its internal water pump after the heating or hot water has been turned off to safely cool down the heat exchanger. S.08 Status Your boiler is taking a short, programmed break to prevent it from turning on and off too frequently, which helps save energy and protect its internal parts. S.10 Status Your boiler is simply letting you know that someone has turned on a hot tap and it is currently busy heating water for your shower or sink. S.11 Status Your boiler is performing a routine start-up check by running the internal fan before the burner ignites. S.13 Status Your boiler is currently struggling to light the flame it needs to provide heating and hot water. S.14 Status Your boiler is not showing an error; it is simply displaying a status message to let you know that the burner is currently active and heating your water. S.15 Status Your boiler is continuing to run its internal components after the heating or hot water has been turned off to safely cool down the system. S.16 Status Your boiler's fan is running longer than necessary to clear out exhaust gases, which may temporarily stall the start-up process. S.17 Status Your boiler is continuing to run its internal pump after the heating or hot water has turned off to help cool down the internal components. S.20 Status Your boiler is temporarily pre-heating the internal water to ensure you get hot water quickly when you turn on a tap. S.21 Status Your boiler is performing a routine start-up check by running its internal fan before lighting the burner. S.22 Status Your boiler is performing a routine check of the internal pump to ensure water is flowing correctly before it starts the main heating process. S.23 Status Your boiler is currently struggling to light the flame it needs to provide heating and hot water. S.24 Status Your boiler is operating normally; this is a status message indicating that the burner is currently lit and heating your water. S.25 Status Your boiler is staying in a cooling-down mode because it thinks the internal temperature is still too high after the heating or hot water has turned off. S.26 Status Your boiler's fan is staying on longer than it should after the heating or hot water has been turned off. S.27 Status Your boiler is continuing to run the pump for a short period after the heating has switched off to safely move excess heat away from the internal components. S.28 Status Your boiler is taking a short, programmed break to prevent it from turning on and off too frequently, which protects the internal parts from unnecessary wear. S.30 Status Your boiler is working fine but hasn't started the heating because your external thermostat or timer is currently telling it to stay off. S.31 Status Your boiler is currently set to provide hot water only, and the central heating has been disabled because it is in summer mode. S.32 Status Your boiler has temporarily paused operation because it has detected very cold temperatures or an unusual fluctuation in the fan speed, often caused by strong winds or a blocked flue. S.34 Status Your boiler is not broken; it has simply noticed the temperature is very low and is running briefly to prevent the internal pipes from freezing. S.36 Status Your boiler is working fine, but your external thermostat or programmer isn't telling it to turn the heating on. S.42 Status Your boiler has paused its heating process because an external control or smart accessory is preventing it from firing up. S.53 Status Your boiler has temporarily paused because the water temperature is rising too quickly or unevenly, suggesting a circulation issue or a sensor fault. S.54 Status Your boiler has sensed that there isn't enough water moving through the system to heat up safely, so it has shut down to protect itself. S.76 Status Your boiler has paused because it is waiting for a stable reading from the internal water pressure sensor. S.96 Status Your boiler is temporarily pausing to perform a routine check on its internal temperature sensors before it can provide heating or hot water. S.97 Status Your boiler is temporarily pausing to check the system's water pressure before it starts up to provide heating or hot water. S.98 Status Your boiler is temporarily pausing because it has detected a suspicious temperature difference and is double-checking that its heat sensors are working correctly before it continues.