Glow-worm F9 Fault Guide for Homeowners: Meaning, Symptoms, Safety, Actions, Causes and Prevention
In your Glow-worm boiler, the F9 fault code is a warning of low water pressure. The signs of the F9 fault are inconsistent water temperature and the boiler shutting down abruptly. The main risk of the F9 fault is overheating, which can damage your boiler. The main causes are leaks within your heating system, or faults in the water pressure sensor and its connecting PCB. Pay attention for leaks and every now again check the pressure of your boiler. Schedule an annual maintenance visit with a boiler engineer, too. Always use a Gas Safe registered engineer for repairs for safety and compliance.
Meaning of the Glow-worm F9 Fault
The F9 fault code on a Glow-worm boiler indicates your boiler has detected low water pressure within your heating system. It is a common issue that can affect the operation and efficiency of your boiler. Low water pressure means the boiler doesn’t have sufficient water to heat. This means you may not get hot water and your radiators and heating system may not heat up to normal temperatures.
What are the risks of the F9 fault?
The primary risk associated with the F9 fault is overheating of the boiler. Insufficient water pressure can cause problems. The heat exchanger may not get enough water to cool down. This can lead to overheating. This can harm the boiler and in severe cases it may be unsafe. This is due to the risk of leaks of hot water or steam.
Can the F9 fault affect my heating system?
Yes, the F9 fault can prevent the normal function of your heating system. Low water pressure can lead to uneven heating, with some radiators not warming up at all. It can also cause the boiler to lock out. This is a safety feature that shuts down the boiler for faults, preventing further damage or danger. This – rather inconveniently – does lead to no hot water and cold showers for you, though!
Is it possible for a homeowner to resolve the F9 fault on their own?
In some cases, homeowners can resolve the F9 fault by repressurizing their boiler. This means adding water via the boiler’s filling loop to increase the pressure, normally to between 1 and 1.5 bar. You’ll find instructions in the user manual to do this. You can also watch this video from Glow-worm:
If adding pressure does not clear the fault, or the fault recurs, you need help. Contact a Gas Safe registered engineer to investigate. There’s something else going on.
Symptoms of the Glow-worm F9 Fault
The first symptom of the F9 fault code are radiators that feel lukewarm or cold, despite the boiler running. Second, the boiler may shut down unexpectedly and need to be reset by hand before it will operate again. Finally the boiler’s pressure gauge on the front panel will often show a reading below 1 bar. The normal operational range is usually between 1 and 1.5 bars.
How can I tell if my boiler’s reduced performance is due to the F9 fault?
Check the boiler’s pressure gauge, if the pressure is below 1 bar, it is likely an F9 fault. If refilling the boiler does not fix it, or the pressure drops soon after, it’s pretty sure the boiler has an F9 fault.
Does the F9 fault code appear immediately when there is a problem?
No, the F9 fault code does not always appear immediately. The boiler may need to go through a few cycles before the fault code is displayed on your control panel.
How To Recognise The F9 Fault on Different Types of Glow-worm Boiler
Glow-worm Combi Boilers
Glow-worm Combi boilers show the F9 fault on the digital display of the control panel. Combi boilers might also show swings in hot water temperature. These could be a sign of changing pressure levels in the system.
Glow-worm System Boilers
System boilers will show the F9 code in a similar manner to combi boilers. You might also notice that the system takes longer than usual to heat up. You may hear more noise from the boiler unit or the pipes. This noise shows that the boiler is struggling due to low pressure.
Older Non-Digital Glow-worm Boilers
On older models without a digital display, symptoms may include less obvious signs. These signs include noisy operation, especially rumbling or banging noises. These noises suggest boiling (kettling) due to low water flow. The absence of a digital fault display means that diagnosing is more difficult. You can use the pressure gauge and noise, but calling in an engineer is the best course of action.
What to Do When Your Glow-Worm Boiler Shows the F9 Fault
The first step to take when your Glow-worm boiler displays the F9 fault is to consult the user manual. This will provide specific guidance and include safety instructions. Here’s a general approach to dealing with the F9 fault:
- Check the Pressure Gauge. The first step is to look at the boiler’s pressure gauge. If it shows a reading below 1 bar, the system definitely needs repressurising.
- Repressurise your boiler. You can do this by following your boiler’s manual. The usual method is to use the filling loop. This allows more water into the system.
- Reset the boiler. After adding pressure, reset it following the manufacturer’s instructions. See if this clears the fault code.
Should I turn off the boiler if I see the F9 fault?
Yes, it’s wise to turn off the boiler before attempting any kind of maintenance, including repressurising. This ensures your safety and prevents any further potential damage to the boiler.
How do I check for water leaks?
Inspect visible piping, radiators, and the area around the boiler for any signs of water leaks, such as dampness or water stains. Pay special attention to joints as these are the most common sources of leaks.
Where can I find the filling loop to repressurize my boiler?
For most boilers, you will find the filling loop underneath the boiler or near the base. Check your manual for boiler-specific instructions. The filling loop has a metal or plastic hose with one or two valves that you can open by hand. These valves allow water into the boiler’s closed water heating system.
Should I shut off the gas supply when dealing with the F9 fault?
No, you don’t need to shut off the gas when dealing with a low-pressure fault. But, you should if you smell gas or suspect a gas leak. In such cases, turn off the gas immediately and contact a professional.
Always follow your boiler’s user manual. For any procedures not in the user manual, or if you’re unsure about doing them, you must contact a Gas Safe engineer. They will ensure the work is done safely and correctly
The Three Major Causes of the F9 Fault
The F9 fault has three main causes.: water leaks, a bad water pressure sensor, or problems with the boiler’s circuit board (PCB) affecting accurate pressure sensing.
Cause 1 – Water Leaks
Water leaks in the central heating system lead to a drop in water pressure, triggering the F9 fault. Leaks can occur from radiator valves, connections, or damaged and corroded pipes.
How can I detect water leaks in my system?
Look for damp patches on walls, floors, or ceilings along with examining the radiator and piping areas for any signs of moisture. Having to regularly repressurise your boiler also suggests there may be a leak.
Cause 2 – Faulty Water Pressure Sensor
The sensor monitors the system’s pressure and reports back to the boiler control unit. If the sensor fails or becomes blocked with debris, it can falsely report low pressure. This leads to a false report of the F9 fault.
What are the signs of a faulty water pressure sensor?
Common signs include erratic boiler behaviour. This can be things like shutting down randomly. Or, failing to start heating despite enough pressure. Also, if repressurizing the system doesn’t fix the fault, the sensor might be the problem.
3. Issues with the PCB
The PCB is the boiler’s brain. It gets inputs from sensors and makes sure the boiler runs safely and well. A malfunctioning PCB can misinterpret correct pressure readings as being too low, resulting in the F9 error.
How do I know if my Glow-worm boiler PCB is malfunctioning?
A faulty PCB can cause incorrect fault codes. It can also cause intermittent boiler operation and unresponsive boiler controls. A professional diagnosis is necessary to confirm a PCB issue because it is a complex fault.
Preventing Future F9 Faults
To prevent the Glow-worm F9 fault from recurring, you must fix the root cause. Follow this up with annual maintenance to reduce the risk of further faults. Below are key preventative measures.
Routine Maintenance
Regular servicing by a qualified technician prevents many common boiler issues. This includes those that lead to the F9. An annual check helps to keep your heating system and boiler working as designed. This includes the pressure sensor and PCB.
How often should I service my boiler to prevent faults?
It’s recommended to service your boiler annually. This helps catch issues early and maintains the boiler’s efficiency and safety.
Monitor Water Pressure
Occasional checks of the boiler’s pressure gauge can alert you to changes in pressure. These changes might show a leak or a failing part.
What should the water pressure be on my Glow-worm boiler?
The normal operating water pressure for most Glow-worm boilers is between 1 and 1.5 bars. Refer to your specific model’s manual for the exact pressure range.
Check for Leaks in Your Central Heating
Keep an eye open for signs of leaks from your heating system. These may occur from radiators, pipes, or the boiler itself.
How can I check for leaks most effectively?
If you think that leaks are likely, check for wet spots on walls, floors and other areas where pipes run. Look for rust or corrosion around pipe fittings and boiler connections. Also, keep an eye on your water bill for unexpected increases, which can be a sign of hidden leaks.
How do I maintain my boiler?
You can’t service boilers yourself, it’s just not safe. But, you can dust around the boiler. Keep the area around it clean and well-ventilated. For maintenance and internal checks and repairs, always use a Gas Safe registered engineer.
These measures will not only prevent the F9 fault. They will also extend your boiler’s life and boost its performance. Regular attention and professional servicing are the keys to a reliable heating system.
Safety Disclaimer
Working on gas appliances without the right qualifications is dangerous and illegal. It can lead to exposure to carbon monoxide, gas leaks, explosions and fires. Always use a certified Gas Safe registered engineer for anything beyond what is in your user manual. Unqualified interventions can lead to accidents, invalidate warranties, and break the law. Don’t take the risk.