Glow-worm boiler error codes

If your Glow-Worm boiler is displaying an unfamiliar error code, don’t panic - you're not alone. Whether you're a homeowner dealing with a sudden heating issue or a landlord trying to keep tenants warm, these fault codes are your boiler’s way of telling you that something’s wrong. The good news is that many of these issues are easy to understand and, in some cases, can be fixed — if you know what the codes mean. 

In this guide, we’ll walk you through the most common Glow-Worm boiler error codes, explain what they indicate, and help you decide whether it’s a quick fix or something that requires a qualified engineer. 

At Maintracts Services Ltd, we’ve been providing expert boiler repairs in London since 1974. Our Gas Safe registered engineers are experienced with Glow-Worm boilers and other major brands, allowing us to diagnose and resolve specific error codes and faults quickly. Whether you’re facing a minor sensor issue or a complete system failure, we deliver fast, reliable repairs at competitive prices. We prioritise safety, efficiency, and restoring your heating with minimal disruption. 

Call us on 020 8682 2244 to speak with our experienced team about your Glow-Worm boiler today! 

 

 

Why Do Glow-Worm Boilers Display Error Codes?

Glow-Worm boilers are built with safety and efficiency in mind. When something isn’t working correctly, be it low water pressure, overheating, or sensor faults, the boiler shuts down or enters a lockout mode to prevent further damage. These errors are flagged by alphanumeric codes or flashing LEDs that tell you exactly what went wrong.

Understanding these codes can help you:

• Troubleshoot simple issues yourself (like topping up water pressure).
• Know when to call a boiler engineer.
• Prevent future boiler breakdowns.

 

Common Glow-Worm Boiler Error Codes And What They Mean

Betacom Range

The Betacom series is one of Glow-Worm’s most popular ranges, commonly found in homes throughout the UK. Here are some frequent fault indicators:

• Red LED On: Boiler lockout due to low water pressure. Try increasing the pressure to around 1.5 bar, then reset.
• Red LED Flashing: Boiler overheat. Check overheat stats—this usually requires a technician.
• Yellow LED Flashing: Turn the domestic hot water (DHW) and central heating (CH) knobs to the correct settings.
• Green LED Off: No power. Check your fuse and whether the boiler is receiving 230V.

 

Glow-Worm Error Codes

Glow-Worm models, such as the Betacom4, Ultracom, Flexicom, and Xtramax HE, use alphanumeric fault codes.

Here are some of the most common Glow-Worm boiler error codes and their meanings:

• F.00: Flow temperature sensor
• F.10: Flow temperature sensor short circuit
• F.12 and F.91: Cylinder temperature sensor short circuit
• F.13: Domestic hot water cylinder temperature sensor short circuit
• F.20: Safety switch-off – overheating temperature reached
• F.22: Safety switch-off – low water pressure in the boiler
• F.23: Safety switch-off – temperature difference too significant (NTC1/NTC2)
• F.24: Safety switch-off – temperature rise too fast
• F.25: Safety switch-off – flue gas temperature too high
• F.27: Safety switch-off – fault in flame detection
• F.28: Ignition is unsuccessful when starting up
• F.29: Flame loss
• F.32: Fan frost protection function active – fan speed outside the tolerance values
• F.33: Fan frost protection function active – air pressure switch fault
• FA9: eBUS fault – voltage too low
• F.61: Gas valve control system fault
• F.82: Gas valve switch-off control fault
• F.83: EEPROM fault – electronics defective
• F.64: Electronics/sensor/analogue-to-digital converter fault
• F.85: Electronics temperature is too high
• F.67: Value sent back by ASIC is incorrect (flame signal)
• F.88: Unstable flame (analogue input), underfloor heating contact or gas valve fault
• F.70: Invalid product code (DSN)
• F.71: Flow/return temperature sensor
• F.72: Deviation in the water pressure sensor/return temperature sensor
• F.73: Water pressure sensor not connected or has short-circuited
• F.74: Electrical problem in the water pressure sensor. For reliable electrical service, contact us for assistance!
• F.75: Pressure sensor fault
• F.78: The safety cut-out in the primary heat exchanger is defective
• F.77: Fault: Condensate or smoke
• F.78: Interruption to domestic hot water (DHW) outlet sensor at external controller
• F.83: Burner temperature sensor fault
• F.84: Flow/return temperature sensor fault
• F.85: Temperature sensor fault
• F.87: Electrode fault
• F.89: Pump fault

Connection: No communication between the printed circuit board (PCB) and the user interface

In many cases, these faults can be attributed to sensor malfunctions, inadequate circulation, or electrical issues. It’s best to consult a qualified heating engineer, especially for electrical or gas-related issues.

 

Quick Fixes For Common Boiler Issues

Here are a few things you can check before calling an expert:

1. Low Water Pressure (F22)

Check your pressure gauge—it should read between 1.0 and 1.5 bar. If the level is low, use the filling loop to top up the system, then reset the boiler.

2. Ignition Fault (F28)

Ensure your gas supply is on, reset the boiler, and check for drafts or blocked flues.

3. Power Issues

If the LED is off, your boiler may not be getting power. Check your fuse box and any visible fuses on the unit itself.

 

While some errors are user-serviceable, others require a Gas Safe registered engineer. You must immediately contact a professional if:

• You notice frequent overheating or ignition loss.
• There are gas valve faults (F26/F77).
• You suspect a PCB or electronic fault (F61, F64, F70).
• The boiler displays multiple errors or locks out repeatedly.