Glow-worm F23 Fault: Meaning, Symptoms, Actions, Costs, Causes, Prevention
The Glow-worm F23 boiler fault means a temperature issue. It detects an imbalance in water circulation between the flow and return pipes. You may see fluctuating temperatures, reduced heating, or an error code on your boiler’s control panel. When this fault appears, reset your boiler. Then, check for blockages or airlocks. If the issue persists, a professional inspection is required. Fixing the F23 fault usually costs £80 to £300. It depends on whether cleaning, repairs, or part replacements are needed. Causes of this issue include sludge build-up, a faulty pump, incorrect pipe sizing, or air trapped within the system. Flush the system, use inhibitors, and service it yearly. This will help prevent this fault. Always contact a Gas Safe-registered engineer for repairs. It is both dangerous and illegal to work on a boiler without proper certification. The next section explains the F23 fault in more detail, helping you understand why it happens and how to address it effectively.
Meaning of the Glow-worm F23 Fault
The F23 fault on a Glow-worm boiler signals a temperature imbalance between the flow and return pipes. The flow pipe carries heated water from the boiler to the radiators, while the return pipe brings cooler water back to be reheated. An F23 error occurs when the temperature difference between these pipes exceeds the boiler’s safe limit. This fault often results from restricted water flow, faulty pump operation, or sludge build-up. Glow-worm boilers monitor temperature changes to heat efficiently. An F23 fault means the heat transfer is not working as expected.
What causes the temperature imbalance that triggers an F23 fault?
An F23 fault occurs when the water returning to the boiler is significantly cooler than the water leaving it. The boiler expects a controlled temperature drop of 10-20°C. A larger drop indicates circulation problems. Common causes include sludge accumulation in pipes or radiators, a failing circulation pump, or airlocks preventing water from moving effectively.
Why does Glow-worm include a temperature differential sensor?
Glow-worm boilers use a sensor to maintain efficient heating. It prevents system strain by monitoring the temperature difference. If the flow water heats too quickly while the return is too cool, the boiler shuts down. This prevents overheating, inefficiency, and damage to internal parts.
Can a blocked radiator cause an F23 fault?
Yes, a blocked radiator can reduce water circulation, leading to an excessive temperature differential. If water cannot flow freely through the radiators, the return pipe will carry much cooler water back to the boiler, triggering the F23 error.
Does an F23 fault mean my boiler is broken?
No, an F23 fault indicates a system imbalance rather than a complete boiler failure. The issue typically relates to water circulation problems rather than a fundamental mechanical fault in the boiler itself. However, ignoring the fault can lead to further damage if overheating occurs.
What should I check first if my boiler shows an F23 fault?
Start by feeling your radiators to check for cold spots, which may indicate sludge or air build-up. Then, ensure your system’s pressure is within the recommended range (typically 1-1.5 bar). If the fault persists, a professional may need to inspect the circulation pump and pipework for blockages or mechanical issues.
The next section details the F23 fault’s symptoms. It will help you spot warning signs before a system failure.
Symptoms of the Glow-worm F23 Fault
An F23 fault on a Glow-worm boiler presents clear warning signs that indicate a heating system imbalance. The most noticeable symptom is inconsistent radiator heating, where some radiators stay cold while others overheat. Your boiler may display the F23 error code on the control panel, often accompanied by flashing warning lights. Water temperature fluctuations at taps and showers suggest that heat is not circulating properly within the system. You may also hear unusual noises, such as gurgling or banging, caused by trapped air or restricted water flow. If the boiler overheats, it may shut down automatically as a safety measure, leaving your home without heating or hot water.
How To Recognise The F23 Glow-worm Fault on Different Types of Boilers
Glow-worm Combi Boilers
Combi boilers heat water on demand, so an F23 fault can result in fluctuating hot water temperatures at taps and showers. The heating system may struggle to warm radiators evenly, causing hot and cold patches throughout your home. The boiler’s digital display will show the F23 fault code, and some models may lock out until the issue is resolved.
Glow-worm System Boilers
System boilers rely on a separate hot water cylinder, so the F23 fault affects radiator heating more than water temperature. You may notice radiators heating unevenly or taking longer than usual to warm up. The boiler’s built-in pump may become noisy due to increased strain, and the control panel will display the F23 code.
Older Non-Digital Glow-worm Boilers
Older Glow-worm boilers without digital displays may not show a fault code but will still exhibit symptoms of poor circulation. Radiators may heat unevenly, with some staying cold despite the boiler running. You might hear loud noises from the boiler or pump, indicating restricted water flow. If the boiler overheats, it may shut down unexpectedly, requiring a manual reset.
The next section suggests actions for the F23 Glow-worm fault. It will help you decide if a reset or a repair is needed.
What to Do When Your Glow-worm Boiler Shows the F23 Fault
If your Glow-worm boiler displays the F23 fault, follow a structured approach to identify and resolve the issue. First, reset the boiler using the manufacturer’s instructions, as this may clear a temporary fault. Next, check your radiators for cold spots, which may indicate sludge build-up or trapped air affecting circulation. Bleeding the radiators can improve water flow, but if the problem persists, further investigation is needed. Ensure your boiler’s pressure is within the recommended range, typically 1-1.5 bar, as low pressure can worsen circulation issues. If your system continues to show the F23 fault after these steps, professional servicing is required.
Safety Warning: Do not open the boiler casing, adjust internal components, or attempt complex repairs. Only perform checks and actions outlined in your boiler’s instruction manual. Always use a Gas Safe-registered engineer for inspections or repairs involving gas or electrical components.
How to reset a Glow-worm boiler after an F23 fault?
Locate the reset button on your boiler’s control panel and press it for a few seconds. The boiler should attempt to restart, but if the fault reappears, further investigation is needed.
Should I turn my boiler off if it displays the F23 fault?
Yes, if your boiler overheats, makes loud noises, or repeatedly shuts down, turn it off to prevent damage. Restart only after checking system pressure and bleeding radiators, or after a Gas Safe engineer inspects the system.
Where do I check my boiler’s pressure?
Check the pressure gauge on the front of your boiler. The needle should sit between 1-1.5 bar. If it is below this range, you may need to top up the system using the filling loop.
How to tell if a blocked radiator is causing the F23 fault?
Feel the radiator from top to bottom. If the bottom is hot but the top remains cold, air is trapped and bleeding may help. If the radiator is cold in patches or entirely cold, sludge may be blocking circulation, requiring a power flush.
Should I shut off the gas supply if my boiler has an F23 fault?
No, an F23 fault relates to water circulation, not gas supply. There is no need to turn off the gas unless you smell gas, hear hissing, or suspect a leak. If you detect a gas leak, turn off the gas at the meter and call the National Gas Emergency Service immediately.
How to check for water leaks that may cause an F23 fault?
Inspect the area around the boiler, pipework, and radiators for signs of water leaks. Damp patches, drips, or corrosion indicate a problem. Leaks can lower system pressure and worsen the F23 fault.
The next section describes the major causes of the F23 fault in more detail, helping you understand why the issue occurs and how to prevent it.
Cost to Repair Glow-worm F23 Fault
The cost to repair an F23 fault on a Glow-worm boiler depends on the underlying issue and required repairs. Minor fixes, such as bleeding radiators or repressurising the system, cost nothing if you complete them yourself. Professional bleeding or a simple system flush costs between £80 and £150, depending on labour charges. If the issue stems from a faulty pump, expect to pay between £200 and £400 for a replacement, including parts and labour. A full power flush to remove sludge and debris from the system costs between £300 and £600, depending on the number of radiators. The maximum cost occurs when multiple components, such as the pump and sensors, need replacing, which can exceed £800.
Regular maintenance reduces the likelihood of expensive repairs by preventing sludge build-up and ensuring proper water circulation. A boiler cover service plan, which includes repairs and servicing, can help manage unexpected costs.
The 5 Major Causes of the Glow-worm F23 Fault
The F23 fault on a Glow-worm boiler occurs when the temperature difference between the flow and return pipes exceeds safe limits. This imbalance happens due to restricted water circulation, component failure, or system inefficiencies. The five major causes include sludge build-up, airlocks, a faulty circulation pump, incorrectly sized pipework, and a blocked heat exchanger. Each of these issues affects how efficiently hot water moves through the system, leading to overheating or uneven heating.
1. Sludge Build-Up in the System
Sludge consists of rust, dirt, and debris that accumulate in radiators and pipework over time. This build-up restricts water flow, causing the return pipe to carry water that is too cold compared to the flow pipe. As a result, the boiler registers an F23 fault. Sludge also forces the boiler to work harder, increasing energy consumption and reducing efficiency. A power flush removes this debris, restoring proper circulation and preventing further damage.
2. Airlocks in the System
Air trapped within the heating system prevents water from circulating properly. When air pockets form, they block water movement, leading to uneven heating and excessive temperature differences between the flow and return pipes. Airlocks often occur after refilling or repressurising the system. Bleeding radiators releases trapped air and restores normal water circulation, helping to prevent the F23 fault.
3. Faulty Circulation Pump
The circulation pump moves hot water from the boiler to the radiators and back. If the pump fails or operates at a reduced speed, water moves too slowly, causing the return pipe to carry water that is significantly cooler than expected. Common signs of a failing pump include noisy operation, radiators heating unevenly, or the boiler frequently shutting down. Replacing the pump resolves the circulation issue and prevents the F23 fault from recurring.
4. Incorrectly Sized Pipework
Pipework that is too narrow restricts water movement, leading to temperature differentials that trigger the F23 fault. Older heating systems often have smaller-diameter pipes that struggle to handle modern boilers’ water flow requirements. If the flow rate is too low, the system cannot balance temperatures effectively. Upgrading to wider pipes improves circulation and ensures the boiler operates within safe temperature limits.
5. Blocked Heat Exchanger
The heat exchanger transfers heat from the boiler’s burner to the water circulating through the system. If it becomes blocked by limescale or debris, heat transfer efficiency drops, causing the water in the flow pipe to overheat while the return water remains too cold. This temperature imbalance results in the F23 fault. A Gas Safe engineer can descale or replace the heat exchanger if blockages cause significant heating issues.
The next section explains how to prevent the F23 fault, helping you avoid costly repairs and maintain an efficient heating system.
Preventing Future Glow-worm F23 Faults
Regular maintenance keeps your boiler running efficiently and reduces the risk of an F23 fault. Annual servicing by a Gas Safe engineer keeps the pump, pipework, and heat exchanger in good condition. A professional service includes checking for sludge build-up, flushing the system if needed, and ensuring correct water pressure.
Using a boiler service contract provides scheduled maintenance and early detection of circulation issues. Adding a central heating inhibitor prevents sludge formation, while installing a magnetic filter captures debris before it clogs pipes. Bleeding radiators when air accumulates also improves water circulation and helps prevent temperature imbalances.
Disclaimer
Any work beyond basic operation described in the user manual should only be carried out by a Gas Safe-registered engineer. Attempting to repair or modify a boiler without proper qualifications risks damage, inefficiency, and safety hazards. Always consult a professional for repairs, servicing, or major system adjustments.