The most common Glow-worm boiler error codes homeowners and landlords across Edinburgh see are F22 for low water pressure, F28 for ignition failure, F29 for flame loss during operation, and F75 for pump or pressure sensor issues.
These codes lock the boiler out until the fault is cleared, leaving the property without heating or hot water. Understanding them quickly helps you decide whether a simple top-up will restore service or whether a Gas Safe engineer is needed.
At The Edinburgh Boiler Company we install new boilers for homeowners and landlords across every Edinburgh postcode from EH1 to EH55 and surrounding towns including Balerno, Bonnyrigg, Dalkeith, Linlithgow, Musselburgh, Penicuik and South Queensferry.
If repeated Glow-worm codes are becoming a regular problem on an older appliance, a modern efficient replacement often delivers better long-term reliability and lower running costs.
Glow-Worm Boiler Error Codes: A Quick Overview
Glow-worm boiler error codes give a clear snapshot of what has gone wrong so you can act fast. The table below covers the codes most often seen on Energy, Ultimate, Betacom and Ultracom models along with a short description of each.
| Code | Concise Description |
| F22 | Low water pressure in the system |
| F28 | Ignition failure at start-up |
| F29 | Flame lost during operation |
| F75 | No pressure change detected when pump starts |
| F20 | Overheating safety cut-out |
| F32 | Fan fault |
| F9 | Low pressure or circulation issue |
| F27 | Flame detection fault |
| F61 | Gas valve control fault |
What Causes Glow-Worm Boiler Error Codes?
Glow-worm boiler error codes and how to fix them depend on the specific fault, but most stem from pressure loss, ignition problems, circulation issues or component wear. The sections below explain each common code in everyday language, list the usual causes, and give practical numbered steps you can take safely.
F22 Low Water Pressure
F22 low water pressure means the boiler has detected that the water level in the heating system has dropped below the safe minimum, usually under 0.8 bar. Without enough water the pump cannot circulate heat properly and the boiler risks damage, so it shuts down. This is the code most homeowners can resolve themselves.
Typical causes include a small leak at a radiator valve or joint, water lost when radiators were bled, natural evaporation over time, or a failing expansion vessel. In many Scottish homes the pressure simply needs a top-up after a period of heavy use.
How to fix:
- Check the pressure gauge on the front of the boiler. It should sit between 1.0 and 1.5 bar when the system is cold.
- Locate the filling loop, usually a flexible silver hose or two small taps under the boiler.
- Slowly open the taps to let mains water in until the gauge reaches about 1.2 bar.
- Close the taps firmly and press the reset button for a few seconds.
- Watch the pressure over the next few days. If it drops again you likely have a leak and need a Gas Safe engineer.
F28 Ignition Failure
F28 ignition failure means the boiler has tried several times to light the burner and has not succeeded, so it locks out for safety. No flame means no heat and no hot water. Common causes are an interrupted gas supply, a frozen condensate pipe in cold weather, dirty or worn ignition electrodes, low gas pressure, or a faulty gas valve.
This code is especially frequent during Scottish winters when external condensate pipes can freeze overnight.
How to fix:
- Confirm other gas appliances such as the hob still work. If they do not, check the gas meter for credit or contact your supplier.
- In freezing weather, carefully pour warm (not boiling) water over the external condensate pipe to thaw any ice, then insulate it.
- Press and hold the reset button for three to five seconds and wait.
- Only attempt one reset. If F28 returns, switch the boiler off and call a Gas Safe registered engineer. They will test gas pressure, clean or replace electrodes and check the condensate route.
F29 Flame Loss During Operation
F29 flame loss during operation means the boiler lit successfully but the flame went out while it was running and could not re-ignite. The result is the same lockout as F28. Causes often include fluctuating gas pressure, a partially blocked flue, wind affecting the flue terminal, a dirty flame sensing electrode, or problems with the gas valve.
It can also follow a temporary interruption that clears itself after a reset.
How to fix:
- Check that the external flue terminal is clear of leaves, nests or debris.
- Make sure the gas supply is stable by testing other appliances.
- Attempt one careful reset.
- If the code reappears, do not keep resetting. A Gas Safe engineer needs to examine the flame sensor, flue path and gas valve to restore safe operation.
F75 Pump Or Pressure Sensor Fault
F75 pump or pressure sensor fault means the boiler expected to see a small rise in pressure when the circulating pump started but detected nothing. The system therefore shuts down to avoid overheating.
This is a very common code on older Energy and Ultimate models. Usual causes are a seized pump after a long summer of inactivity, air trapped in the pump, a blocked or faulty pressure sensor, or sludge in the system.
How to fix:
- Check the system pressure is between 1.0 and 1.5 bar and top up if needed.
- Listen for the pump humming when the boiler tries to start. Silence or grinding can point to a seized impeller.
- Try one reset after confirming pressure.
- Persistent F75 requires a Gas Safe engineer. They may free the pump, clean the sensor or recommend a power flush if sludge is present. Repair costs typically fall between £150 and £350 depending on parts.
F20 Overheating Safety Cut-Out
F20 overheating safety cut-out means the boiler temperature has risen too high and the safety limiter has switched everything off. This protects the heat exchanger and other components.
Causes include poor circulation from a stuck pump, low water pressure, air locks, a blocked heat exchanger or a faulty temperature sensor. Leaving the boiler to cool is the first safe step.
How to fix:
- Turn the boiler off completely at the isolator and allow it to cool for at least 30 minutes.
- Check and top up the system pressure if it is low.
- Bleed any radiators that feel cold at the top to release trapped air.
- Restore power and attempt one reset.
- If F20 returns, call a Gas Safe engineer. Ongoing overheating can indicate deeper circulation or heat-exchanger problems that need professional attention.
F32 Fan Fault
F32 fan fault means the boiler cannot confirm that the fan is running at the correct speed. The fan is essential for safe removal of combustion gases, so the boiler locks out. Causes include a worn fan motor, loose wiring, a blocked air intake or flue, or a faulty speed sensor. This is not a code to ignore.
How to fix:
- Check the external flue terminal for any obvious obstruction and clear it if safe to reach.
- Ensure the area around the boiler is free of dust or items blocking vents.
- Attempt one reset after any external clearance.
- If the code remains, switch the boiler off and contact a Gas Safe engineer. Fan replacement or wiring work must be carried out by a qualified professional.
Ready For Dependable Heating Without The Error Codes?
Living with repeated Glow-worm boiler error codes can leave any household or rental property without reliable heat, especially through the colder months. While many faults can be resolved, older boilers that keep throwing codes often cost more in call-outs and parts than a straightforward replacement.
At The Edinburgh Boiler Company we specialise in new boiler installations for homeowners and landlords across Edinburgh and the surrounding areas. A modern high-efficiency system arrives with a long manufacturer warranty, lower energy use and far fewer unexpected lockouts.
Request your free no-obligation new boiler quote today and let us help you move past the frustration of fault codes for good.
Frequently Asked Questions
How often should a Glow-worm boiler be serviced to reduce error codes?
An annual service by a Gas Safe registered engineer is the best way to catch wear, clean electrodes and check pressure sensors before they trigger codes. Many manufacturers also require regular servicing to keep the warranty valid.
Can a power cut cause Glow-worm boiler error codes to appear?
Yes. A sudden power interruption can leave the control board in an unexpected state or allow air into the system. After power returns, a single reset often clears temporary codes, but any that reappear need proper diagnosis.
Do Glow-worm error codes differ between combi and system boilers?
The most common F codes such as F22, F28, F29 and F75 appear on both combi and system models. System boilers may show additional cylinder-related codes, but the core pressure, ignition and pump faults remain the same.
Is it worth repairing an older Glow-worm that keeps showing error codes?
If the boiler is more than 12 to 15 years old and major components are failing, replacement usually works out cheaper over five years once you factor in energy savings and avoided call-out fees. A Gas Safe engineer can give a clear cost comparison.
What should I do if I smell gas when a Glow-worm error code appears?
Turn the boiler off at the isolator, open windows, do not use electrical switches, and call the National Gas Emergency number 0800 111 999 immediately. Do not attempt any further resets or work.
