Glowworm Fault Codes: Common Causes & How to Fix Them
If your boiler has stopped working and is displaying one of the Glowworm fault codes, don’t panic. These fault codes are built into the boiler to help identify problems quickly, making it easier to troubleshoot minor issues or determine when professional assistance is needed.
Some faults can be resolved with simple checks, such as topping up the boiler pressure or resetting the system. Others indicate more serious issues that should only be diagnosed and repaired by a Gas Safe registered engineer.
In this guide, we’ll explain the most common Glowworm fault codes, what they mean, their likely causes, and the steps you can take to resolve them safely.
Table of contents
What Are Glowworm Fault Codes?
Glowworm boilers continuously monitor their internal components. If the boiler detects a fault, it displays an error code on the control panel.
These Glowworm fault codes help identify issues such as:
- Low water pressure
- Ignition failures
- Overheating
- Fan problems
- Faulty sensors
- Gas valve faults
- Pump issues
Understanding these codes can save time and help you determine whether a simple reset will solve the issue or if professional repairs are required.
Common Glowworm Fault Codes Explained
F1 – Boiler Failed to Ignite
What it means
The boiler has attempted to ignite several times but has failed and entered lockout mode.
Possible causes
- Frozen condensate pipe
- Ignition fault
- Gas supply interruption
- Faulty ignition components
How to fix it
- Reset the boiler.
- Check that your condensate pipe isn’t frozen.
- Ensure your gas supply is working.
- If the fault returns, contact a Gas Safe engineer.
F4 – Ignition Failure
What it means
Like F1, this code indicates repeated ignition failure.
Possible causes
- Gas supply turned off
- Empty prepaid gas meter
- Faulty ignition electrode
- Gas valve issues
How to fix it
- Check your gas meter.
- Test another gas appliance.
- Reset the boiler.
- If unsuccessful, arrange a professional repair.
F9 – Pressure Sensor Fault
What it means
The boiler has detected an issue with the system pressure.
Possible causes
- Low system pressure
- Faulty pressure sensor
- Debris inside the sensor
- Sludge within the heating system
How to fix it
- Check the pressure gauge.
- Top up pressure to approximately 1.0–1.5 bar.
- Reset the boiler.
- If the fault persists, the pressure sensor may require replacement.
F22 – Low Water Pressure
What it means
The boiler has shut down because system pressure is too low.
Possible causes
- Water leak
- Recently bled radiators
- Expansion vessel issue
How to fix it
- Check the pressure gauge.
- Repressurise the boiler.
- Reset the boiler.
- If pressure continues to drop, contact an engineer.
F25 – High Flue Gas Temperature
What it means
The boiler cannot safely remove the heat it is producing.
Possible causes
- Blocked heat exchanger
- Restricted circulation
- Pump problems
- Dirty heating system
How to fix it
- Check boiler pressure.
- Lower the flow temperature to around 65°C.
- Reset the boiler.
- Arrange a professional inspection if the fault returns.
Step-by-Step Troubleshooting for Glowworm Fault Codes
Time needed: 5 minutes
Before calling an engineer, try these basic checks:
- Reset the Boiler
Locate the reset button and press it according to your user manual.
- Check Boiler Pressure
Ensure pressure is between 1.0 and 1.5 bar when the system is cold.
- Check Your Gas Supply
Make sure your gas supply is on.
Test another gas appliance if available.
Check your prepayment meter has sufficient credit. - Inspect the Condensate Pipe
During winter, frozen condensate pipes are a common cause of boiler lockouts.
- Check for Blocked Vents or Flues
Remove any obvious debris from around the flue terminal.
- Contact a Gas Safe Registered Engineer
If the boiler repeatedly displays Glowworm fault codes after basic troubleshooting, professional diagnosis is recommended.
How to Prevent Glowworm Fault Codes
Regular maintenance can help avoid many common faults.
Schedule an Annual Boiler Service
A yearly service helps identify worn parts before they fail and keeps your boiler operating efficiently.
Monitor Boiler Pressure
Check the pressure gauge every month and maintain it within the recommended range.
Insulate External Condensate Pipes
This helps prevent freezing during cold weather.
Bleed Radiators Correctly
After bleeding radiators, always check and restore the boiler pressure if needed.
Keep the Flue Clear
Ensure the flue terminal remains free from leaves, debris, and obstructions.
Conclusion
Most Glowworm fault codes are designed to protect your boiler and make fault diagnosis easier. While issues such as low pressure or a frozen condensate pipe can often be resolved at home, faults involving gas valves, electronics, ignition systems, or combustion should always be investigated by a Gas Safe registered engineer.
Understanding what these fault codes mean allows you to act quickly, minimise downtime, and keep your heating system operating safely and efficiently.
Frequently Asked Questions
Glow-worm boiler fault codes (displayed as “F.XX”) indicate specific malfunctions. While some require a Gas Safe engineer, others have simple DIY fixes.
The F75 typically means the pressure sensor can’t confirm the pump is running either because the sensor is blocked with sludge, or the pump has seized. We carry genuine Glow-worm pressure sensors on the van for a same-visit fix in most cases.
The usual suspects are trapped air in your heating system, loose wiring connections, or a faulty PCB. While you can check for simple fixes like bleeding your radiators or verifying water pressure, it’s best to leave the repairs to a Gas Safe registered professional.
