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Last updated: 8th February, 2024


Glow-Worm F27 Error Code - How To Fix

Glow-Worm F27 Error Code - How To Fix

Key takeaways

  • The F27 error code indicates a fault in the boiler's flame detection system.
  • Diagnosing and troubleshooting the F27 error requires identifying the root cause and making the necessary adjustments or replacements.
  • If in doubt, homeowners should contact a professional gas engineer to resolve the issue safely and effectively.

The F27 error code can result from several underlying issues, ranging from low gas pressure to a faulty ignition system. Addressing these problems typically requires diagnosing the precise cause and making appropriate adjustments or replacements.

Glow-Worm F27 Error Code - How To Fix

Glow-Worm boilers are renowned for their efficiency and reliability, but like any appliance, they can encounter issues from time to time. 

One common fault code homeowners may come across is the F27 error code, which indicates a problem with the boiler's flame detection system.

Understanding the nature of this error and the potential causes can help you take the necessary steps to resolve the issue and restore your boiler's functionality.

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The F27 error code can result from several underlying issues, ranging from low gas pressure to a faulty ignition system. Addressing these problems typically requires diagnosing the precise cause and making appropriate adjustments or replacements. 

However, the complexity and potential risks associated with working on a gas boiler mean that it's often best to seek the assistance of a professional gas engineer when confronted with this error code.

Understanding Glow-Worm Boiler and F27 Error Code

Glow-Worm is a renowned budget brand in the heating industry, known for their reliable and efficient boilers. Among the various models they offer, it's not uncommon for issues to arise, as with any appliance. 

One such issue that may occur in a Glow-Worm boiler is the F27 error code. This section will provide a concise overview of the F27 error code, its implications, and the necessary steps for a potential resolution.

The F27 error code signifies a flame detection fault. This occurs when the boiler's flame sensor is unable to detect a flame despite having sufficient gas supply. As a safety feature, the boiler's operation is halted to avoid gas leaks or explosions. There are numerous potential causes for this fault, including malfunction of the flame sensor, ignition problems, or gas valve defects.

When troubleshooting this error, a few components should be examined:

  1. Flame sensor: Over time, residue and dirt can accumulate on the sensor, impairing its detection capabilities. Carefully cleaning the sensor might resolve the issue.

  2. Ignition leads: Damaged or loose leads can lead to poor ignition, and consequently, the F27 error code. It's essential to check the connections, ensuring they are secure and in good condition.

  3. Gas valve: If the valve is faulty, it may not supply the required amount of gas to the burner. A professional should assess the gas valve to determine if it's functioning correctly.

While these steps might help in identifying the cause of the F27 error code, it's crucial to remember that boiler repairs, especially those involving gas-related components, should be performed by a Gas Safe registered engineer. Therefore, if the error persists despite the basic troubleshooting, it's best to contact a professional for assistance.

In conclusion, the F27 error code in a Glow-Worm boiler may be indicative of problems with the flame detection system. Addressing the issue promptly could prevent potential hazards, ensuring a safe environment and efficient functioning of the boiler. Remember to consult a professional if the problem persists, as they possess the expertise to carry out necessary repairs.

Common Glow-Worm Boiler Faults

Glow-worm boilers are known for their reliability and efficiency. However, like any other appliances, occasionally issues arise, and error codes help identify the problem. Understanding various fault codes can help you take appropriate steps to fix the issue. In this section, we will discuss some common error codes and their meanings.

Error Codes and Their Meaning

Here is a brief list of Glow-Worm boiler fault codes with their corresponding descriptions:

  • F.00: Ignition fault

  • F.10: Flow thermistor fault

  • F.11: Return thermistor fault

  • F.12: Flame loss in the gas valve during operation

  • F.13: Combustion fault

  • F.20: Safety thermostat operated

  • F.22: Insufficient water pressure

  • F.23: Overheating fault

  • F.24: Low water pressure

  • F.25: Maximum flow temperature sensor

  • F.28: Loss of flame during operation

  • F.29: No ignition

  • F.32: Fan speed fault

  • F.61: Gas-Water valve connection fault

  • F.64: Primary heat exchanger fault

  • F.67: Flame not detected

Some other fault codes for Glow-Worm boilers are listed below:

  • F.70: System communication fault

  • F.71: Flow sensor fault

  • F.72: Flow-return sensor difference issue

  • F.73: Water pressure sensor fault

  • F.75: Water pressure switch issue

  • F.77: Condensate pump fault

  • F.83: Flow temperature sensor fault

  • F.84: Return temperature sensor fault

  • F.85: Calibration error

  • F.91: Unspecified software issue

Note that this list is not exhaustive and other codes may apply to specific models.

It's essential to take these Glow-Worm boiler fault codes seriously and consult a professional Gas Safe registered engineer if you are unsure about the problem or fix. Regular maintenance can help prevent common issues and prolong the life of your boiler.

Diagnostics and Troubleshooting Glow-Worm F27 Error Code

Recognising Symptoms of F27 Error

It is important for homeowners and technicians to recognise the symptoms of the F27 error code. This error code manifests itself when a Glow-Worm boiler detects a flame detection fault. Key indicators of the F27 error occurring are:

  • Loss of flame during operation

  • Frequent interruptions of heating and hot water supply

  • Fluctuation of flame signal

  • Boiler display showing the "F27" error code

When experiencing these symptoms, proceed to the technical causes of the F27 error.

Technical Causes of F27 Error

There are several technical causes of the F27 error. In order to resolve it, understanding these potential causes is crucial:

  1. Overheat: The boiler may have overheated due to insufficient water flow

  2. Low Water Pressure: There could be a problem with the water pressure in the system

  3. Circulation Fault: The circulation pump might be malfunctioning or blocked

  4. Incorrect Air Pressure: The gas valve or flue may be obstructed, resulting in incorrect air pressure

  5. Permanent Temperature Difference: The boiler's temperature sensor might be faulty or damaged, causing a continuous temperature difference

Awareness of these causative factors can aid in the troubleshooting process. However, it's important to take safety precautions during the process.

Safety Measures while Troubleshooting

When attempting to diagnose and resolve the F27 error code, adhering to safety measures is paramount:

  • Always switch off the boiler's power supply and wait for it to cool down before initiating any work.

  • If you're not confident or qualified, consult a registered gas engineer to inspect and fix your boiler.

  • Ensure the work area is well-ventilated, as incorrect air pressure can cause potentially dangerous situations.

  • Test the boiler's functionality thoroughly after applying any fixes to ensure the F27 error is resolved and other potential issues are not present.

By following the provided steps and troubleshooting recommendations, you can diagnose and address the F27 error code on a Glow-Worm boiler. With a focus on safety and a thorough understanding of the issue, you'll be well-equipped to restore your boiler's functionality.

When to call a Gas Engineer

Glow-Worm boilers are known for their reliability and performance. However, like any other household appliance, they can sometimes develop faults. One such fault is the F27 error code, which indicates a flame detection issue. In this section, we will delve into situations when it's necessary to call a Gas Engineer to fix this error code.

Fixing Glow-Worm F27 Error Code

The F27 error code in Glow-Worm boilers could be caused by several factors, including loose wires and connections, a defective flame sensor, or issues with the gas valve. Attempting to fix these issues without proper expertise could potentially lead to more complications or even become a safety hazard. Therefore, it's crucial to know when to call a Gas Safe registered engineer for assistance.

  1. Gas Valve Problems: If a gas valve issue is causing the F27 fault code, it's essential to contact a gas engineer since this issue could lead to serious consequences if not resolved correctly.

  2. Defective Flame Sensor: As per the manufacturer's guidelines, a faulty flame sensor could trigger the F27 error code. In such cases, it's best to seek assistance from a qualified professional.

  3. Loose Wires or Connections: Sometimes, a simple fix like securing loose wires and connections could resolve the F27 error code. However, in the absence of adequate knowledge, it's prudent to consult a Gas Safe engineer for this task.

While it's always tempting to save costs by troubleshooting boilers independently, this could prove to be counterproductive in the long run. When faced with an F27 error code, it's highly recommended to seek the expertise of a Gas Engineer. They are equipped to diagnose the issue accurately and ensure the boiler functions optimally.

Additionally, a Gas Engineer should be sought for new boiler installations. They have the requisite experience and know-how to perform the installation securely and efficiently, adhering to safety guidelines.

In conclusion, when dealing with the Glow-Worm F27 error code or new boiler installations, it's crucial to engage the services of a Gas Safe registered engineer to ensure safety, professionalism, and peace of mind.

Maintenance and Prevention

Regular maintenance and prevention can help to minimise the occurrence of the Glow-Worm F27 error code. With the proper upkeep, your central heating system will operate more efficiently, reducing the risk of faults and improving overall performance.

One crucial aspect to monitor is the water pressure within the system. Over time, fluctuations can cause issues, so it's essential to maintain the correct pressure level. This can be done by following these simple steps:

  1. Check the pressure gauge on your boiler.

  2. If the pressure is low, open the filling loop to top up the system.

  3. Monitor the gauge closely and close the filling loop once the desired pressure is reached.

For those with underfloor heating contact, it's important to ensure the system's temperature difference never exceeds the specified range. Keeping the heating system clean and free of debris will further assist in minimising temperature imbalances.

Another aspect to consider is the potential for overheating. Over time, components within the boiler can wear out or become clogged with limescale, leading to insufficient heat transfer. Periodic servicing is vital in detecting issues before they escalate. Additionally, the use of a specialised boiler inhibitor can help prevent limescale build-up and other deposits.

In case of any unusual occurrences or behaviour in your central heating system, it's crucial to check for faults regularly. This includes examining the boiler's flame and ensuring it ignites correctly. A competent heating engineer should be contacted to resolve any detected issues efficiently and safely.

New Boiler Costs

Boilers can be a daunting purchase for many people as they’re an appliance with a lot of responsibility, providing heat for you and your family is something you want to get right. Boilers aren’t exactly a quickly disposable item either, potentially lasting you a decade.

Effectively, new boiler cost can be split into two segments: the first is the actual boiler itself (unit price), and the second is the cost of the boiler being installed (set up) in your property by an expert engineer. 

Here at iHeat, we want to remove all of this undue stress and make the decision making process of upgrading to a new central heating system, as easy as possible.

Boiler costs can vary depending on a number of factors including their brand, model, fuel, output, warranty, labour and installation type. Typically a new boiler will cost between £1,845 and £3,500, below is a list of average boiler installations offered by iHeat (guide only).

Installation Type

Price (inc VAT)

Combi to combi swap


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System to combi conversion


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New boiler install


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Back boiler to a combi


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System to system


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Some location factors that can influence the price of your new boiler

You will be given a specific quote from the boiler installation company based on:

  • The type of home you have (i.e. terraced, semi-detached, etc.)

  • How many bedrooms you have

  • How many bathrooms you have

  • Your postcode and specific location

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Frequently Asked Questions

What does F27 mean on a Glow-Worm boiler?

F27 error code on a Glow-Worm boiler indicates a flame detection fault. This is usually due to a malfunction in the flame monitoring system or damage to the boiler's electronics.

What is the F27 fault on a Meridian condensing boiler?

The F27 fault on a Meridian condensing boiler signifies the same issue as with Glow-Worm boilers—a flame detection fault. Potential causes include malfunctioning flame sensors, electronics damage, or issues with the ignition system.

What does F22 mean on my Glow-Worm boiler?

F22 error code on a Glow-Worm boiler suggests low water pressure within the system. This can result from multiple causes, such as leaks, insufficient water, or air trapped in the system. To fix this issue, it's necessary to identify the root cause and address it accordingly.

What is the F20 error on a Glow-Worm boiler?

An F20 error code on a Glow-Worm boiler indicates an overheating issue. This could result from factors such as poor water circulation, a malfunctioning pump, or a blocked heat exchanger. In any case, identifying and resolving the specific issue is crucial before the boiler can be safely used again.

How do I reset my Glow-worm boiler?

To reset a Glow-Worm boiler, locate the reset button, typically found on the front panel of the boiler. Press and hold the reset button for a few seconds, then release it. The boiler should then restart and attempt to operate normally. If issues persist after resetting, it's advisable to consult a heating engineer.

Why is my Glow-worm boiler not firing up?

Several reasons can lead to a Glow-Worm boiler not firing up, such as a lack of power, gas supply issues, or a fault in the ignition system. Examining these components to detect and resolve any issue is important to restore the boiler's functionality.

How long should a Glow Worm boiler last?

A well-maintained Glow Worm boiler can last around 10-15 years. To ensure optimal performance and longevity, regular servicing by a certified engineer, and addressing any faults promptly is highly recommended.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.