Glow Worm Boiler Error Codes: Causes & Fixes

Glow Worm boiler error codes appear as an F followed by a number, such as F22 or F75, on the digital display of modern models. Older boilers may show a red flashing light with a number of flashes instead. Each code is a built-in diagnostic message that tells the control board to lock the boiler out for safety until the problem is fixed.

This guide explains the most common Glow Worm fault codes, what they mean, why they happen, and the safe steps to take before booking a Gas Safe engineer.

Most Common Glow Worm Fault Codes

What Does Glow Worm Error Code F22 Mean?

Glow Worm error code F22 means the system water pressure has dropped too low, usually below 0.5 bar.

Causes of F22 Low Pressure

• A small leak on radiators, pipework, or the pressure relief valve.
• Bleeding radiators without topping up afterwards.
• A faulty expansion vessel or filling loop.

How to Fix F22

1. Locate the filling loop, the grey or blue handles or flexible silver hose under the boiler.
2. Open both valves slowly until the gauge reaches 1 to 1.5 bar.
3. Close tightly and wipe away any drips.
4. The boiler usually resets itself within 30 seconds. If pressure drops again within days, call an engineer to find the leak.

What Does Glow Worm Error Code F75 Mean?

Glow Worm error code F75 is a well-known, and often misunderstood, fault that means the boiler cannot detect a pressure rise when the pump runs, usually because of a stuck or failed pump or a faulty pressure sensor.

Causes of F75

• A seized or worn pump, very common after 7 to 10 years.
• A blocked pressure sensor pipe.
• Airlocks or sludge stopping water movement.

How to Fix F75

• Bleed all radiators and top up pressure first, which occasionally clears it.
• Listen for the pump. No humming usually means a failed pump.
• A replacement Grundfos pump on most Glow Worm models costs £180 to £280 fitted.
• A sensor pipe clean or sensor swap is cheaper, typically £90 to £140.

What Does Glow Worm Error Code F28 Mean?

Glow Worm error code F28 means the boiler tried to light but failed to establish a flame, an ignition lockout. This can stem from a problem with the gas supply, a faulty igniter, or a blocked flue. Regular maintenance and troubleshooting help identify the root cause and restore proper functioning. For a fuller understanding, the glow worm boiler fault code explained page covers a closely related code worth comparing against F28.

Causes of F28

• No gas supply, or very low gas pressure.
• A frozen condensate pipe, a classic winter cause.
• Dirty ignition electrodes or a dirty flame probe.
• A faulty gas valve.

How to Fix F28

• Check that other gas appliances in the home still work.
• Thaw any frozen condensate pipe with warm water and insulate it afterwards.
• Reset once. A persistent F28 nearly always needs an engineer to clean electrodes or test gas pressure.

What Does Glow Worm Error Code F13 Mean?

Glow Worm error code F13 points to a problem with the main printed circuit board, or PCB, or its wiring.

Causes of F13

• Water ingress onto the PCB, often from a leak above the boiler.
• Power surge damage.
• Age-related component failure.

How to Fix F13

• Power off for 10 minutes, which sometimes clears a temporary glitch.
• A full PCB replacement is usually required, typically £220 to £350 fitted.

What Does Glow Worm Error Code F14 Mean?

Glow Worm error code F14 is an overheat lockout.

Causes of F14

• Sludge or limescale blocking the heat exchanger.
• A pump running too slowly.
• Air in the system.

How to Fix F14

• Bleed radiators and top up pressure.
• Reset the boiler after 20 minutes of cooling.
• Recurring F14 usually means a power flush or pump replacement is needed.

What Does Glow Worm Error Code F83 Mean?

Glow Worm error code F83, on newer models, means the boiler detects no temperature rise when heating, in other words, water isn’t circulating properly. Maintaining optimal performance is crucial for any heating system, and understanding Glow Worm boiler efficiency ratings against Vaillant helps homeowners make informed decisions, since checking these ratings ensures the boiler operates efficiently while minimising energy consumption and costs.

Addressing an issue like F83 promptly also improves overall system reliability and longevity. When comparing Glowworm vs Worcester Bosch reviews, it’s worth weighing energy efficiency, reliability, and user satisfaction, since performance can vary based on specific heating needs and installation conditions.

Causes of F83

• Airlocks.
• A blocked system or heat exchanger.
• Pump failure.

How to Fix F83

• Bleed the system thoroughly.
• An engineer power flush or pump replacement resolves the vast majority of cases.

What Do Glow Worm Error Codes F61, F62, F63, and F64 Mean?

These codes all relate to the gas valve control circuit or PCB feedback.

How to Fix F61 to F64

These are engineer-only repairs, usually a gas valve replacement or a PCB swap.

FAQs

Can I still get hot water if a fault code is showing?

Most Glow Worm fault codes put the boiler into full lockout, so there’s no heating and no hot water until the code is cleared.

Customers often share their experiences through GlowWorm boiler customer testimonials, frequently highlighting the reliability of their systems and a responsive customer service team when a fault does come up. Reviewing the Glow worm boiler coverage details explained page helps clarify what’s included in a warranty or support plan before assuming a repair will be covered, which can save an unwelcome surprise if the boiler ever does need attention.

How many times is it safe to reset my Glow Worm boiler?

Only once or twice, and only after fixing the obvious cause, such as a frozen pipe. Repeated resets can damage components and may affect any future warranty claim.

If the same code keeps returning despite a reset, that’s a sign the underlying fault hasn’t actually been resolved, and it’s time to call an engineer rather than keep resetting.

Do Glow Worm boilers store a history of fault codes?

Yes, pressing and holding the spanner or reset button for 5 seconds on most models opens the fault history menu, showing the last 10 codes recorded.

This history can be genuinely useful for an engineer diagnosing an intermittent fault, since it shows the pattern of what’s happened rather than just the single code showing on the day of the visit.

Will a magnetic filter stop future error codes?

Yes, fitting a MagnaClean or similar magnetic filter meaningfully reduces F75, F83, and overheat faults by catching sludge before it can block the pump or sensor.

It’s a relatively low-cost addition that pays for itself over time by cutting the number of sludge-related callouts a boiler is likely to need.

Are Glow Worm boilers still supported after Vaillant bought the brand?

Yes, parts and technical support remain strong. Glow Worm has been part of the Vaillant Group since 2001, and many engineers carry common spares for Energy, Betacom, and Ultracom models on their vans.

Founded in 1934 at the Derwent Foundry in Derbyshire, Glow Worm has over 80 years of UK heating history behind it, which helps explain why parts availability and installer familiarity remain solid despite the brand no longer operating independently.

What’s the safest way to identify a fault code if the display only shows flashes, not text?

Older Glow Worm models without a digital display use a red flashing light, where the number of flashes in a sequence corresponds to a specific fault code listed in the boiler’s manual.

Counting the flashes carefully and checking them against the model-specific manual, rather than assuming based on a similar newer model, gives the most reliable reading before deciding whether to attempt a DIY fix or call an engineer.

Should I still book an annual service if the boiler seems to be running fine with no fault codes?

Yes, an annual service catches developing issues like early pump wear or a slow pressure leak before they escalate into a fault code and a full lockout. A quick check of the Gas Safe Register confirms an engineer’s credentials before booking the service.

Skipping the annual service can also affect warranty cover, since most manufacturers require proof of regular servicing to keep a claim valid.