Glowworm F28 Fault Code: Causes and Step-by-Step Fix Guide
If your boiler displays the Glowworm F28 fault code, it means there has been a failed ignition attempt. In simple terms, your boiler is trying to ignite but isn’t successfully lighting the burner.
The challenge with the Glowworm F28 fault code is that it doesn’t point to a single issue there are multiple possible causes. In this guide, we’ll break them down and show you how to troubleshoot safely.
Table of contents
What Does the Glowworm F28 Fault Code Mean?
he F28 fault code indicates an ignition failure. Your boiler is unable to ignite due to a problem with gas supply, airflow, or internal components.
As a safety precaution, the boiler will enter lockout mode to prevent unburned gas from accumulating.
Common Causes of the Glowworm F28 Fault Code
Based on manufacturer documentation and widely referenced heating industry sources, here are the most common causes:
Gas Pressure Issues
- Insufficient gas supply
- Air trapped in the gas line
- Frozen gas regulator (in cold weather)
- Gas mains not suitable for a newer, more powerful boiler
Flue or Airway Blockage
- Blocked flue pipe
- Obstruction in the condensate pipe
- Debris or damage restricting airflow
Faulty or Misadjusted Gas Valve
- Incorrect gas flow to the burner
- Inconsistent or no gas supply
Ignition Component Faults
- Faulty ignition electrode
- Damaged ignition leads
- Worn or wet electrical components
Faulty Spark Generator
- No spark produced to ignite gas
- Requires replacement in most cases
Burner Debris or Blockage
- Carbon buildup blocking the burner jet
- Prevents proper gas flow and ignition
PCB (Printed Circuit Board) Failure
- Boiler’s control system not sending correct signals
- Can cause multiple faults, including ignition failure
Frozen Condensate Pipe
- Common in winter
- Ice blockage prevents normal boiler operation
Step-by-Step Fix for Glowworm F28 Fault Code
Time needed: 5 minutes
Before calling an engineer, you can try these safe troubleshooting steps:
- Check Your Gas Supply
Ensure your gas is turned on
Test other gas appliances (e.g., hob)
Check if your meter has credit - Reset the Boiler
Locate the reset button
Press and hold for a few seconds
Allow the boiler to restart
Only attempt this once repeated resets can worsen the issue. - Inspect the Condensate Pipe
Look for freezing or blockages
Thaw gently with warm (not boiling) water if frozen - Check the Flue and Airflow
Ensure the flue outlet is not blocked
Remove any visible debris (if safely accessible) - Look for Obvious Signs
Listen for ignition clicks
Check for unusual noises or smells - Call a Gas Safe Registered Engineer
If the Glowworm F28 fault code persists, professional help is required. An engineer will:
Test gas pressure and supply
Inspect ignition components
Clean or replace the burner
Diagnose PCB or gas valve faults
Never attempt internal boiler repairs yourself it is unsafe and illegal without proper certification.
When to Call a Professional
You should contact an engineer if:
- The fault continues after a reset
- There is no gas supply or ignition
- You suspect electrical or internal faults
- The boiler repeatedly locks out
Preventing the Glowworm F28 Fault Code
To reduce the risk of future ignition faults:
- Schedule annual boiler servicing
- Keep condensate pipes insulated
- Ensure proper gas supply and pressure
- Address minor faults early
- Keep the flue and vents clear
Conclusion
The Glowworm F28 fault code is a common but potentially complex issue linked to ignition failure. While simple checks like gas supply and resetting the boiler may resolve it, deeper problems often require expert diagnosis.
Acting quickly helps restore heating and prevents more costly repairs down the line.
Frequently Asked Questions
An F28 fault code on a boiler (most commonly on Vaillant models) indicates an ignition failure. The boiler has attempted to ignite the burner but could not detect a flame and has locked out for safety.
The official explanation for an F28 fault is “The flame signal was not detected during the ignition phase,” which can be caused by several different factors, such as a frozen condensate pipe, which you can fix yourself. You’ll typically find your condensate pipe exiting at the nearest outside wall from your boiler.
The F22 error on a Glow-worm boiler indicates low system water pressure (often dropping below 1.0 bar). This usually happens due to a small leak in the system, trapped air after bleeding radiators, or natural evaporation.
