Glow-worm Boiler Fault Codes, Causes and Fixes
Seeing a strange error code on your Glow-worm boiler? Don’t panic — many problems can be resolved quickly, and some even without needing a heating engineer. Whether you’re in Wokingham, Earley, Woodley, or Shinfield, we’ve got you covered.
At Thermo-Tec Plumbing & Heating, we help local homeowners get their heating and hot water back on fast. Here's everything you need to know about Glow-worm fault codes, resets, and when to call in help.
Glow-worm Boiler Fault Codes Explained
Glow-worm boilers like the Betacom, Energy, and Ultimate models all use a fault code system to signal what’s wrong. Here are the most common ones we encounter:
Fault Code F1 – Low Water Pressure
What it means: The system doesn’t have enough water pressure to operate safely.
Causes:
Bleeding radiators
Leaking pipework
Faulty pressure sensor or expansion vessel
DIY Fix:
Check the pressure gauge (should be 1.0–1.5 bar)
Re-pressurise using the filling loop
Reset the boiler
💡 If this keeps happening, get a heating engineer to check for slow leaks or valve issues.
Fault Code F28 / F29 – Ignition Fault or Flame Loss
What it means: Your boiler can’t light or the flame has gone out.
Causes:
Frozen condensate pipe (in cold weather)
Faulty flame sensor
Air in gas supply
Blocked flue
What to try:
Check gas supply is active
Inspect outdoor pipes for freezing
Press the reset button
If these errors return, your ignition unit or sensor may need replacing.
Fault Code F75 – Pressure Sensor / Pump Fault
What it means: The boiler isn’t detecting a pressure rise when the pump runs.
Causes:
Faulty pump
Blocked or broken pressure sensor
Air in the system
Fix: Needs a Gas Safe engineer. We'll test the sensor and pump and flush out trapped air if needed.
Fault Code F22 – Dry Fire / No Water
What it means: The boiler is running with no water in the system.
Fix:
This is similar to F1 — check pressure and refill as needed. If it keeps returning, professional help is needed.
When to Call Thermotec your Local Gas Safe Engineer in Wokingham
If you're seeing recurring fault codes, unusual noises, smells, or a total system shutdown, it's time to call a qualified heating engineer.
At Thermo-Tec Plumbing & Heating, we’re Gas Safe registered and experienced with Vaillant fault codes. We cover Wokingham, Lower Earley, Woosehill, and surrounding villages.
Need a Glow Worm Boiler Repair in Wokingham?
If your Vaillant boiler is showing a fault code or refusing to fire up, we’re here to help.
Call Thermo-Tec today on 07850116944 for Glow Worm boiler repairs in Wokingham and surrounding areas.
Glow-worm Boilers: Frequently Asked Questions
1. What does the F28 or F29 fault code mean on my Glow-worm boiler?
The F28 and F29 codes are the most common errors for Glow-worm Energy and Ultimate models. They indicate an ignition failure—essentially, the boiler tried to light but failed (F28) or lost the flame during operation (F29). In the Wokingham area, this is often caused by a blocked condensate pipe during winter, a faulty gas valve, or a dirty spark electrode. Always check that your gas meter hasn't been accidentally shut off before calling an engineer.
2. How do I fix the F22 "Low Water Pressure" fault?
If your Glow-worm display is flashing F22, your system pressure has dropped below the safety limit. You can usually fix this yourself by locating the filling loop (a silver braided hose) underneath the boiler. Open the blue or black plastic valves slowly until the digital display or manual gauge reads 1.5 bar. Once the pressure is restored, the code should disappear, and the boiler will fire up. If this happens frequently, you may have a slow leak or a failing expansion vessel.
3. Why is my Glow-worm boiler making a loud banging or "kettling" noise?
Loud noises in a Glow-worm boiler are usually a sign of "kettling," often linked to an F75 or F24 fault. This happens when lime-scale or "sludge" builds up in the primary heat exchanger, restricting water flow. This makes the water boil too quickly (like a kettle). As a Wokingham heating specialist, I recommend a professional Powerflush or a chemical system cleanse to clear the debris and restore quiet, efficient operation.
4. Can I reset my Glow-worm boiler myself?
Yes. To reset a Glow-worm boiler, look for the button with a flame symbol with a line through it or a button marked "Reset." Press and hold it for three seconds. If the boiler lockouts again immediately, do not keep resetting it. Repeatedly forcing an ignition can damage the PCB or the burner. If a reset doesn't clear the code, it’s a sign that a safety component has failed.
5. How often should a Glow-worm boiler be serviced to keep the warranty?
To keep your Glow-worm manufacturer warranty valid (which can be up to 10 years on certain models), you must have a Gas Safe registered engineer perform an annual service. During a Thermotec service, we don't just check for safety; we clean the burner, check the expansion vessel pressure, and test the flue gases. This prevents common faults like the F27 or F28 from happening in the first place.
6. My Glow-worm is showing an F75 fault. Is it a major repair?
The F75 code is very common and usually indicates a faulty Pressure Sensor. The boiler needs to see a "pulse" from the pump to know it's safe to fire. If the sensor is blocked with sludge or has failed, it can't see that pulse. While it’s not a "major" engine failure, it does require a part replacement. I carry genuine Glow-worm sensors on my van to get Wokingham homes back up and running in a single visit.