Glow-Worm Boiler Error Codes: Causes & Fixes

The most common Glow-worm boiler error codes UK homeowners and landlords see are F22 or F9 for low water pressure, F28, F1 or F4 for ignition failure (often linked to a frozen condensate pipe), F29 for flame loss during operation, F75 for pump or pressure sensor issues, and F20 for overheating. 

These codes help you work out what needs attention so you can get the heating and hot water back on safely.

Some can be sorted with a quick top-up or thaw, while others need a Gas Safe registered engineer. Knowing what the code means puts you in control and stops small issues turning into bigger bills. Many people find that having reliable boiler cover in place means they can call for help straight away without worrying about the cost of parts or labour when a more serious fault appears.

Glow-Worm Boiler Error Codes: A Quick Overview

Here is a clear snapshot of the Glow-worm boiler error codes you are most likely to see, with a short plain-English note on what each one usually points to.

Codes can vary slightly by model range, so always check your handbook if the display looks different. The table above covers the codes that appear most often across UK homes.

Glow-Worm Boiler Error Codes: Causes & How to Fix

Below you will find dedicated sections for the main Glow-worm boiler error codes. Each one explains what the code means, the usual causes, and clear numbered steps you can take. Safety comes first: if you smell gas, turn the supply off at the meter if it is safe and call the National Gas Emergency Service on 0800 111 999. 

For any gas-related work or if a code returns after a reset, contact a Gas Safe registered engineer.

F22 Or F9 Low Water Pressure

The F22 or F9 error code means the water pressure in your sealed heating system has dropped below the safe operating level. The boiler will not fire until the pressure is restored.

Common causes include a small leak from a radiator valve, pipe joint or pressure relief valve, natural pressure loss after bleeding radiators, or a problem with the expansion vessel.

1. 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).
2. Locate the filling loop (usually a flexible silver hose with two valves under or near the boiler).
3. Open both valves slowly to let mains water in until the gauge reaches about 1.2–1.5 bar.
4. Close both valves tightly.
5. The boiler often resets itself within 30 seconds. If not, press the reset button.
6. Watch the pressure over the next day or two. If it drops again, there is likely a leak that needs professional attention.

Topping up is a simple job most homeowners can do, but repeated drops should not be ignored.

F28, F1 Or F4 Ignition Failure

The F28, F1 or F4 fault code means the boiler has tried to light but has not detected a flame within the safety time limit. Heating and hot water will stop until the fault is cleared.

Typical causes are a frozen or blocked condensate pipe (very common in UK winters), a temporary interruption to the gas supply, a dirty or faulty ignition electrode, low gas pressure, or a problem with the gas valve or spark generator.

1. Check that other gas appliances in the home (hob, fire) are working. If none are, contact your gas supplier or check your meter credit.
2. Look outside for the white plastic condensate pipe. If it feels frozen or has ice visible, pour warm (not boiling) water along its length to thaw it.
3. Once thawed, press and hold the reset button for a few seconds.
4. Listen for the fan starting and the spark attempting to light.
5. If the code returns after one or two resets, switch the boiler off and call a Gas Safe engineer. Do not keep resetting.

A frozen condensate pipe is by far the most frequent winter cause and is often the quickest win.

F29 Flame Loss During Operation

The F29 code means the boiler successfully lit but then lost the flame while running.

Causes include a temporary gas supply interruption, a dirty flame sensing electrode, a problem with the gas valve, or combustion issues. In cold weather the condensate pipe can also play a part.

1. Check other gas appliances are still working.
2. Inspect and thaw the condensate pipe if needed.
3. Reset the boiler once.
4. If the code returns immediately, do not keep resetting. Call a Gas Safe engineer to check the electrodes, gas valve and combustion.

F75 Pump Or Pressure Sensor Fault

The F75 fault code means the boiler cannot detect a rise in pressure when the pump starts. This is often linked to a stuck or failed pump, or a blocked or faulty pressure sensor.

Causes include a seized pump (common after several years), magnetite sludge blocking the sensor pipe, airlocks, or a failing pressure sensor.

1. Check and top up system pressure to 1.0–1.5 bar.
2. Bleed radiators to remove air.
3. Reset the boiler once.
4. If the code returns, an engineer will need to free or replace the pump, or clean/replace the pressure sensor. This is not a DIY job.

F20 Overheating

The F20 error code means the safety system has detected that the water inside the boiler has got too hot and has shut it down.

Common reasons are a stuck or failing pump, restricted water flow, air in the system, sludge build-up, or a faulty temperature sensor.

1. Turn the boiler off and allow it to cool completely (this can take 30–60 minutes).
2. Check system pressure and top up if needed.
3. Make sure all radiator valves are fully open.
4. Bleed any radiators that feel cold at the top.
5. Reset the boiler once it is cool.
6. If F20 returns, do not keep using the boiler. Call a Gas Safe engineer to check the pump, flow and sensors.

F32 Fan Fault

The F32 code indicates a problem with the fan speed or air pressure. The fan is essential for safe combustion and removing flue gases.

Causes include a failed fan motor, wiring issues, a blocked flue, or a faulty air pressure switch.

Do not attempt to repair the fan yourself. Switch the boiler off and arrange for a Gas Safe engineer to diagnose and replace the fan if needed. Running without a working fan is unsafe.

F27 Or F16 Flame Detection Fault

The F27 or F16 error code means the boiler is having trouble detecting the flame properly, even if one is present.

Causes are usually a dirty or faulty flame sensing electrode, a damaged lead, moisture on the electronics, or a PCB issue.

Reset once if the boiler allows it. If the code returns, a Gas Safe engineer will need to clean or replace the electrode and check the related wiring and board.

F00 Or F10 Flow Temperature Sensor Fault

The F00 or F10 fault code points to a problem with the flow temperature sensor (open circuit or short circuit).

Causes include a failed sensor, damaged wiring, or a poor connection.

This is not a DIY fix. Reset once if possible. If the code returns, an engineer will test and replace the sensor or repair the wiring.

F01 Or F11 Return Temperature Sensor Fault

The F01 or F11 code means the return temperature sensor is reading incorrectly.

Causes are similar to the flow sensor: a failed component or wiring problem. An engineer is required to diagnose and replace the part.

F23 Temperature Difference Too Great

The F23 error code means the difference between the flow and return temperatures is larger than expected.

Causes include a blocked or restricted pump, air in the system, closed valves, or switched or faulty sensors.

1. Check and top up pressure.
2. Ensure all valves are open and bleed radiators.
3. Reset once.
4. If it returns, an engineer needs to check circulation and sensors.

Having a boiler cover plan in place can make a real difference when codes like these appear. Instead of facing unexpected call-out and repair costs, you simply report the fault and a qualified engineer is arranged. For many UK homeowners and landlords this peace of mind, plus the included annual service, helps prevent small pressure or sensor issues from becoming expensive breakdowns.

How To Reset A Glow-Worm Boiler Safely

Most Glow-worm models have a clearly marked reset button on the control panel (often marked with a flame symbol). Press and hold it for a few seconds until the display clears or the boiler restarts. Only reset once or twice for the same code. If the fault returns, switch the boiler off and seek professional help. Continuous resetting can put extra strain on components.

When a Glow-Worm Boiler Fault Requires Professional Help

Some Glow-Worm error codes can be resolved with straightforward checks, particularly low-pressure faults such as F22 or F9 and ignition problems caused by a frozen condensate pipe. However, faults involving the boiler’s internal components should be left to a qualified professional.

You should arrange for a Gas Safe registered engineer to inspect your Glow-Worm boiler if:

• F28, F1, F4 or F29 continues to appear after you have checked the gas supply, thawed the condensate pipe if necessary and reset the boiler.
• F75 returns, as this can indicate a problem with the pump, pressure sensor or circulation within the boiler.
• The boiler repeatedly displays F20, F23 or F25, which may point to restricted water circulation, overheating or another internal fault.
• You see fan, flue or flame detection codes such as F32, F27 or F16.
• A temperature sensor or electronics fault continues to appear, including F00, F10, F01, F11 or codes within the F61 to F67 range.
• Your boiler loses pressure repeatedly, continues shutting down or does not operate normally after basic checks.

Avoid repeatedly resetting the boiler in an attempt to clear a persistent fault. An engineer can investigate the specific cause of the error code, test the relevant components and carry out the necessary repairs safely.

How to Prevent Glow-Worm Boiler Error Codes

• Check the system pressure as part of your regular boiler routine: A gradual drop in pressure can eventually trigger faults such as F22 or F9. Checking the gauge periodically makes it easier to spot an ongoing issue before the boiler locks out.
• Watch for early signs of poor circulation: Radiators that remain cold, make gurgling noises or heat unevenly can indicate trapped air or restricted water flow. Dealing with these symptoms early may help reduce the risk of circulation-related faults such as F23, F25 and F20.
• Keep the heating system clean and well maintained: Over time, sludge and magnetite can build up within the system and affect pumps, sensors and water flow. If your heating system shows signs of contamination or poor circulation, have it assessed before it contributes to a more serious fault.
• Have the pump and internal circulation checked if the boiler is getting older: The F75 code can be linked to pump or pressure sensor problems. Unusual humming, vibration or inconsistent heating performance should be investigated before the pump fails completely.
• Protect the condensate pipe ahead of freezing weather: Cold temperatures can cause the condensate pipe to freeze, which may contribute to ignition faults such as F28, F1 or F4. Checking that the pipe is suitably protected before winter can help reduce this risk.
• Make sure your gas supply is not interrupted: If you have a prepayment meter, keep an eye on available credit, and if you notice issues with other gas appliances, address them promptly. Temporary interruptions can contribute to ignition and flame-loss faults.
• Do not ignore intermittent flame problems: If the boiler occasionally cuts out, struggles to maintain a flame or requires frequent resets, have it checked before the issue develops into a recurring F29, F27 or F16 fault.
• Keep the area around the boiler suitable for servicing: Avoid obstructing access to the boiler with fixed cupboards, stored items or other objects that could make routine inspection and maintenance more difficult.
• Schedule professional servicing before the colder months: An annual boiler service can identify developing issues with components such as sensors, the fan, ignition system and pump before increased winter demand places additional strain on the boiler.
• Treat repeated fault codes as an early warning rather than simply resetting them: If the same Glow-Worm error code returns, arrange for the underlying issue to be diagnosed instead of continually clearing the fault. Early attention can help prevent a temporary issue from becoming a complete boiler breakdown.

Protect Your Home From Unexpected Glow-Worm Boiler Faults

While understanding the Glow-Worm boiler error codes such as F22, F28 and F75 can help you identify what may be wrong, unexpected boiler breakdowns can still lead to inconvenient and costly repairs.

With a PlusHeat boiler cover plan, you can protect yourself against the unexpected costs associated with boiler breakdowns and repairs. Depending on the level of cover you choose, PlusHeat plans can help provide protection for your boiler and controls, with more comprehensive options also available for your central heating, plumbing and electrics.

Take a look at our boiler cover plans today and find the right level of protection for your home or rental property, so you can be better prepared when an unexpected Glow-Worm boiler fault occurs.

Frequently Asked Questions 

What should I do if my Glow-worm boiler shows a code that is not listed in the manual?

Note the exact code and any lights or symbols, then check the official Glow-worm support resources or contact a Gas Safe engineer. Different ranges (Betacom, Energy, Ultimate, Ultracom) can use slightly different displays, so matching the full code to your exact model is important.

Can a power cut cause Glow-worm boiler error codes?

Yes. After a power interruption some boilers display a general lockout, communication fault or ERR code. Once power is stable, a single reset often clears it. If the code returns, the control board or wiring may need checking.

How often should I check my Glow-worm boiler pressure to avoid error codes?

A quick look at the pressure gauge once a month is sensible, especially before winter. Aim for 1.0–1.5 bar when the system is cold. Catching a slow pressure drop early helps prevent F22 or F9 from appearing.

Do Glow-worm error codes differ between combi and system boilers?

Many core codes (pressure, ignition, sensors, fan) are shared, but system models may show additional codes related to the cylinder sensor or different hydraulic arrangements. Always refer to the specific handbook for your model.

Is it safe to keep using the boiler if an error code clears after a reset?

Only if the code does not return and the boiler runs normally with stable pressure and even heating. Any recurring code, unusual noises, or smell of gas means stop using it and call a qualified engineer.