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Common Glow Worm Boiler Fault Codes


Lee Devlin

Published on: 24/07/2023
common glow worm boiler fault codes

In the world of boilers, Glow-worm is a well-known and trusted brand. However, like any other appliance, Glow-worm boilers can experience faults from time to time. These faults are typically indicated by error codes that appear on the boiler’s display panel. Understanding these fault codes is crucial for homeowners, as it can help them identify and address any problems with their boiler system.

Here are some common glow worm boiler fault codes:

Boiler Model Fault Codes Cause of Problem
BetacomRed LED OnLockout – low water pressure (increase pressure to 1.5bar) and reset boiler
BetacomRed LED flashingOverheat – check both overheat stats
BetacomYellow LED flashingTurn domestic hot water (DHW) control knob into temperature range and turn central heating (CH) temperature control knob into power (reset position)
BetacomYellow LED onFlame present on the burner
BetacomGreen LED onGreen LED on
BetacomGreen LED offNo power to boiler – Check for 230volts into the appliance, check the fuse on printed circuit board (PCB)
Betacom4 / Ultracom3 cxi / sxi / 35F00 / F10 / F71Flow heating temperature sensor fault
Betacom4 / Ultracom3 cxi / sxi / 35F01 / F11Return heating temperature sensor fault
Betacom4 / Ultracom3 cxi / sxi / 35F20Overheating fault
Betacom4 / Ultracom3 cxi / sxi / hxi / 35 / Flexicom cx / hx / sxF9 / F22Low water pressure (or ignition temperature rise too slow)
Betacom4 / Ultracom3 cxi / sxi / 35F26 / F77Fault in gas valve
Betacom4 / Ultracom3 cxi / sxi / 35 / CI / hxi / Xtramax HEF27 / F16Flame detection fault
All BoilersF28 / F1 / F4Ignition fault (flame detection)
Betacom4 / Ultracom3 cxi / sxi / 35F29Loss of flame during operation
Betacom4 / Ultracom3 cxi / sxi / 35F32Incorrect air pressure
Betacom4 / Ultracom3 cxi / sxi / 35F49EBUS voltage fault
Betacom4 / Ultracom3 cxi / sxi / 35F61 / F62 / F63 / F64 / F65 / F67Fault in the main board
Betacom4 / Ultracom3 cxi / sxi / 35F68Fluctuation of flame signal
Betacom4 / Ultracom3 cxi / sxi / 35F70User interface incompatible with the main board
Betacom4 / Ultracom3 cxi / sxi / 35F72 / F84Permanent temperature difference between flow and return heating sensors
Betacom4 / Ultracom3 cxi / sxi / 35F73 / F74Heating circuit pressure sensor fault
Betacom4 / Ultracom3 cxi / sxi / 35F76Thermal fuse fault
Betacom4 / Ultracom3 cxi / sxi / 35F83Thermal fuse fault
Betacom4 / Ultracom3 cxi / sxi / 35F85Flow and Return heating sensor fault
Betacom4/ Ultracom3 cxi / sxi / 35F86Underfloor heating contact fault
All BoilersERR / F12 / F18User interface fault
Betacom cTemperature 30 flashingFault on central heating (CH) thermistor
Betacom cTemperature 40 flashingFault on DHW thermistor
Betacom cTemperature 50 flashingFault on outside sensor
Betacom cTemperature 60 flashingLow system pressure
Betacom cTemperature 70 flashingFault on APS
Betacom cTemperature 80 flashingOverheat open circuit
Betacom cTemperature 90 flashingFlame or gas failure
Compact e / sNo DHWCheck dhw microswitch / Check external controls, Please test for 230V on switch live contact
Compact e / sNo C/HCheck dhw microswitch if dhw demand led is lit / Check external controls, Please test for 230V on switch live contact
Compact e / sNo C/H but boiler is firingCheck divertor motor and cartridge / Check external controls, Please test for 230V on switch live contact
Compact e / sBoiler locks out within 10 secondsCheck pump proving switch, air pressure switch and overheat state / Check pump proving switch, air pressure switch and overheat stat
Compact e / sPoor burner pressureCheck burner pressure/ignition adjustment pots on PCB
Ci Range (plus) / Si rangeF2Fan/APS
All BoilersF5Overheat Fault
All BoilersF6Central heating flow thermistor
All BoilersF7Domestic hot water thermistor
All BoilersF8Tank thermistor fault
sxi / si / ci (plus) range / Xtramax HEF9Water pressure sensor fault (please contact GW technical department for further information)
All boilersF10Central return flow thermistor
All boilersF11Main board connection fault
Ci (plus) / cxi / hxi / si / sxi rangeF12Connection fault between main printed circuit board (PCB) and display PCB
Ci (plus) / cxi / hxi / si / sxi rangeF13Main pcb connection fault
Ci (plus) / cxi / hxi / si / sxi rangeF14Central heating flow temperature > 95 degrees
Ci (plus) / cxi / si / sxi rangeF15Gas valve stepper motor fault
Ci (plus) / cxi / hxi / si / sxi range / Xtramax HEF17Power supply is less than 170v
Ci (plus) / cxi / hxi / si / sxi range / Xtramax HEF19Central heating thermistor unplugged
Ci (plus) / cxi / hxi / si / sxi range / Xtramax HEF20Software incompatibility
cxi / hxi / sxi range / Flexicom cxF24Central heating return temperature > 90 degrees
cxi / hxi / sxi / Xtrafast 96/120 / Xtrafast 96/120E1F25 / F26 / F11Poor circulation
ci rangeF3Air fault
cxi / sxi / hxi range/ Xtramax HEF2 / F3Fan
cxi / sxi range / Flexicom cx / hx / sx / hxi / Ultracom cxi / cx / hxi / sxi / Ultrapower sxiF3Fan unable to reach ignition speed
Flexicom cx / hx / sx / hxi / Ultracom cxi / cx / hxi / sxiF9Water pressure sensor fault, blocked flow filter or pump fault
Flexicom cx / hx / sxF11Flow and or return thermistor fault
Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxi / Xtramax HEF13PCB memory or sensing fault
Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxi / Xtramax HEF14Gas valve control defective
Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxi / Xtramax HEF15E-bus voltage failure
All boilersF25 / F23Circulation fault
Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiF43Generic error
Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiF70Software incompatible
Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiF73Unable to see pump activate
Flexicom cx / hx / sx / Ultracom cxi / cx / hxi / sxiF77Condensate pump error (optional)
hxi rangeF9Earlier models only (please contact GW technical department for further information)
Ultracom? 35 StoreF02 / F12Hot water temperature sensor fault
Ultracom? 35 StoreF03 / F13 / F79Storage tank temperature sensor fault
Ultracom? 35 StoreF81Overheating of hot water circuit
All UltracomNo display or Erloose connection X51
Xtramax HE RangeF24Cental heating return temperature > 90 degrees
Xtramax HE RangeF25Maximum temperature rise slope
Xtramax HE RangeF26Maximum delta temperature
Xtrafast 96/120 RangeF00No-fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF00No-fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF02Airflow fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF05Overheating
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF06Central heating thermistor/wiring fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF08Storage vessel thermistor/wiring fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF09System pressure sensor fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF10Fan fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF13Main printed circuit board (PCB) fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF14Central heating flow temperature > 97 degrees
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF15Gas mechanism fault
Xtrafast 96/120 Range / Xtrafast 96/120E1 RangeF20Communication fault

*table credit: WarmZilla

Understanding Glow worm boiler fault codes

When it comes to Glow worm boiler fault codes, it’s important to start with the basics. So, what exactly are these fault codes, and why are they significant?

Let’s delve deeper into the world of Glow worm boiler fault codes and explore the fascinating details behind their existence.

What are Glow worm boiler fault codes?

In simple terms, fault codes are alphanumeric codes that indicate specific issues with your Glow worm boiler. These codes provide valuable diagnostic information to both homeowners and heating engineers, making it easier to identify and resolve any problems. When an issue arises, the boiler’s control panel will display a fault code, enabling you to understand the nature of the problem.

Imagine this scenario: you wake up one chilly morning, eagerly anticipating a warm and comforting shower. However, as you turn on the tap, you notice that the water remains cold. Frustration starts to creep in, but fear not – the fault code displayed on your Glow worm boiler’s control panel can provide you with valuable insights into the underlying issue.

Whether it’s a faulty sensor, a blocked pipe, or an ignition problem, these fault codes act as a beacon of hope, guiding you towards a resolution.

Importance of recognising fault codes

Recognising Glow worm boiler fault codes is vital for prompt troubleshooting and resolution of issues. By understanding the fault codes, homeowners can determine whether the problem requires professional assistance or if it is something they can resolve themselves. Identifying the fault codes early on can also help prevent further damage to the boiler system and potentially save on costly repair bills.

Imagine this: you’ve just moved into a new home, and you’re still getting acquainted with the quirks and idiosyncrasies of your Glow worm boiler. Suddenly, a fault code appears on the control panel, leaving you perplexed and uncertain about the next steps to take.

But fear not, for armed with the knowledge of these fault codes, you can embark on a journey of troubleshooting and problem-solving. You might discover that a simple reset or a quick check of the pressure gauge is all it takes to restore your boiler to its former glory.

Moreover, recognising fault codes empowers homeowners to communicate effectively with heating engineers, providing them with accurate information that can expedite the boiler repair process. Instead of stumbling through vague descriptions of the issue, you can confidently relay the fault code, allowing the engineer to arrive prepared with the necessary tools and expertise.

So, the next time you encounter a Glow worm boiler fault code, embrace it as an opportunity to unravel the mysteries within your heating system. With a little curiosity and a willingness to learn, you’ll be well on your way to becoming a boiler troubleshooting expert.

Common Glow worm boiler fault codes

Now that we understand the significance of fault codes, let’s delve into some of the most common Glow worm boiler fault codes and what they mean.

Code F1: Low water pressure

One of the most common issues homeowners face with their Glow worm boiler is low water pressure. Code F1 indicates that the water pressure in the system has dropped below the recommended level. This can be caused by a leak in the system or a problem with the pressure gauge. Homeowners can usually resolve this issue by repressurising the boiler, following the manufacturer’s instructions.

When the water pressure in a Glow worm boiler is too low, it can lead to a range of problems. Firstly, the boiler may struggle to heat the water to the desired temperature, resulting in lukewarm showers and baths. Additionally, low water pressure can cause the boiler to work harder than necessary, leading to increased energy consumption and higher utility bills. It is important for homeowners to regularly check the water pressure gauge on their Glow worm boiler and take action if it drops below the recommended level.

In some cases, low water pressure may be a symptom of a larger issue within the heating system. A leak in the pipes or radiators can cause a drop in pressure, and if left unaddressed, it can result in water damage to the property. Homeowners should inspect their heating system for any signs of leaks, such as damp patches or water stains on walls or ceilings. If a leak is suspected, it is advisable to contact a professional plumber to identify and fix the problem.

Code F4: Ignition fault

If your Glow worm boiler displays code F4, it means there is an ignition fault. This fault code indicates that the boiler is struggling to ignite, which may be due to a faulty ignition electrode, a blocked burner, or an issue with the spark generator. It is advisable to seek professional help to diagnose and rectify the ignition fault.

An ignition fault can be frustrating for homeowners, as it means the boiler may fail to provide hot water and central heating. In colder months, this can be particularly inconvenient and uncomfortable. Ignition faults can have various causes, and it is important to address them promptly to avoid further damage to the boiler. Ignition electrodes can wear out over time and may need replacement. Blockages in the burner can prevent proper ignition and may require cleaning or repair. The spark generator, responsible for creating the spark that ignites the gas, can also malfunction and may need professional attention.

Regular boiler maintenance can help prevent ignition faults and ensure the efficient operation of the Glow worm boiler. Homeowners should schedule annual servicing by a qualified heating engineer who can inspect and clean the ignition components, as well as identify any potential issues before they escalate into major faults.

Code F9: Unrecognised PCB connection

An unrecognised PCB connection is another fault code that Glow worm boilers may display. Code F9 suggests that there is a problem with the Printed Circuit Board (PCB) connection. This could be due to loose wiring or a faulty PCB. In such cases, it is best to contact a qualified heating engineer for assistance with diagnosing and repairing the issue.

The PCB is a crucial component of the boiler’s electrical system, responsible for controlling various functions and ensuring the safe operation of the appliance. When the PCB connection is unrecognised, it can disrupt the communication between different parts of the boiler, leading to malfunctions or complete system failure. Homeowners should avoid attempting to fix PCB issues themselves, as it requires technical knowledge and expertise. A qualified heating engineer will have the necessary skills to diagnose the problem accurately and either repair or replace the faulty PCB.

Regular maintenance and servicing of the Glow worm boiler can help prevent PCB-related faults. During a service, the heating engineer will inspect the PCB for any signs of damage or loose connections. They will also ensure that the boiler’s electrical system meets safety standards and is functioning correctly. By addressing any potential PCB issues early on, homeowners can avoid costly repairs and ensure the longevity of their Glow worm boiler.

Troubleshooting Glow worm boiler fault codes

While some Glow worm boiler fault codes may require professional intervention, there are a few troubleshooting steps homeowners can take to resolve minor issues themselves.

Steps to reset your Glow worm boiler

If you encounter a fault code on your Glow worm boiler, a simple troubleshooting step is to reset the system. This can be done by turning off the boiler, waiting for a few seconds, and then turning it back on again. In some cases, this may clear the fault code and resolve the issue. However, if the fault persists, it is advisable to contact a heating engineer for further assistance.

When to call a professional

While some fault codes can be resolved with basic troubleshooting, there are instances where professional intervention is necessary. If you are unsure about the cause of the fault code or if attempts to resolve it yourself have been unsuccessful, it is recommended to call a qualified heating engineer. They have the expertise and knowledge to diagnose and repair complex boiler issues safely and efficiently.

Preventing Glow worm boiler faults

Prevention is always better than cure, and the same holds true for Glow worm boiler faults. By following a few simple maintenance tips, homeowners can reduce the likelihood of encountering fault codes and ensure the smooth operation of their boilers.

Regular boiler maintenance tips

To keep your Glow worm boiler running efficiently, it is important to carry out regular maintenance tasks. This includes checking the boiler’s pressure regularly, bleeding radiators to remove trapped air, and checking for any leaks or unusual noises. Additionally, keeping the boiler area free from clutter and ensuring proper ventilation can also contribute to its longevity.

Importance of annual boiler servicing

Another crucial aspect of preventing Glow worm boiler faults is scheduling annual servicing. Regular servicing by a qualified professional can help identify any potential issues before they escalate into major faults. A professional service will include checking for gas leaks, cleaning and inspecting components, and ensuring the boiler is operating within safety limits, giving homeowners peace of mind and a well-maintained boiler system.

FAQs about Glow worm boiler fault codes

Finally, let’s address some frequently asked questions regarding Glow worm boiler fault codes.

Can I fix a Glow worm boiler fault code myself?

While some minor issues can be resolved through troubleshooting, it is generally recommended to seek professional assistance when dealing with Glow worm boiler fault codes. Attempting to fix complex issues without proper knowledge and expertise can potentially worsen the problem or compromise safety. It is best to leave faults requiring technical expertise to qualified heating engineers.

How often should I service my Glow worm boiler?

To ensure the optimal performance and longevity of your Glow worm boiler, it is advised to schedule an annual service. Regular servicing allows a qualified professional to inspect and maintain the boiler, identify any potential faults, and carry out necessary repairs or adjustments. By adhering to annual servicing, homeowners can maximise the efficiency and reliability of their Glow worm boiler.


Glow worm boiler fault codes provide homeowners with valuable diagnostic information when issues arise. By understanding these fault codes, homeowners can take appropriate action to troubleshoot and resolve minor issues themselves or seek professional assistance when needed. Performing routine maintenance tasks and scheduling annual servicing are essential in preventing boiler faults and ensuring the efficient and safe operation of your Glow worm boiler. Stay proactive, stay informed, and enjoy a hassle-free heating system.

For professional help and advice, get in touch with the friendly team at Homecure today!

Lee Devlin
Publication date: 24/07/2023

Lee Devlin is the managing director of Homecure Plumbers, London's favourite local plumbing service. Since 2009, Lee's been leading a large team of gas safe plumbing and heating engineers as well as growing a successful business built on quality customer service and workmanship, in a competitive industry within the Capital. He's been in the game for a long time, so he regularly shares his knowledge and experience with the public. His expert tips have been featured in lots of well known publications such as: The Sun, Metro, Insider, Homes And Gardens, Country Living and more!

Read More About Lee Devlin.

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