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Common Glow-worm Boiler Problems & Repair Advice

Rob Wells
By: Rob Wells
Updated: 9th December 2021

This guide to the most common Glow-worm boiler problems will help you through the hard times and could even see you fixing a fault yourself. Should you be in any doubt at all or identify a fault that needs an engineer, you can get a free boiler repair quote with our service.

Common Glow-worm boiler problems

Glow-worm boiler problems Glow-worm error code
Low water pressure 108 or F22
Flame detection fault F16
No heating or hot water 501
Frozen condensate pipe F1, F4, F28 or F29
Loud noises F9
Printed circuit board (PCB) fault F13

Low boiler pressure (108 or F22)

If the pressure gauge on your Glow-worm boiler is showing anything below 1 bar then you may have an issue which can lead to your central heating system not functioning as well as it should. Over time, boilers will gradually lose pressure but a sudden drop could mean there’s a fault somewhere in the system, commonly a leak.

Increasing low boiler pressure

If you spot a leak around the heating system, turn off the water supply and contact a Gas Safe registered engineer, likewise if there’s been a sudden drop in pressure. For any gradual decreases in boiler pressure, it’s possible to repressurise the system yourself by following the steps in our guide to low boiler pressure. If you don’t feel safe doing this or aren’t overly sure about what today, contact a heating engineer to do it for you.

Once the pressure is back up to around 1.5 bar, your Glow-worm boiler should have sufficient pressure to work again. Increase the pressure too much (above 2 bar) and you’ll then have a problem with high boiler pressure, which could damage the unit.

Flame detection fault (Error code F16)

If F16 displays on your boiler, there's a flame detection fault with your boiler.

Turning the hot water tap calls the printed circuit board (PCB) into action, telling the burner to fire up so that the water can be heated, which involves the gas valve supplying sufficient fuel. When the F16 error code appears, there’s an issue preventing this process form happening – either the flame isn’t present or the PCB is failing to detect the flame.

How to fix the F16 error code

Never attempt to fix the F16 error code on a Glow-worm boiler yourself, always hire a Gas Safe registered engineer. There are many potential issues that they will look into, diagnose and be able to repair:

  • Flame sensor damage
  • Faulty PCB
  • Blockage in the burner jet
  • Gas valve issues
  • Blocked flue or condensate pipe

No heating or hot water

There are many potential reasons why there's no heating or hot water in your home, including broken diaphragms and airlocks, failure of motorised valves, issues with the thermostat or low water levels.

How to get the heating and hot water back on

Start out by checking if the boiler pressure is too low (below 1bar) and that the temperature is set high enough for the heating to come on. In addition to these, if you’re on a prepayment meter then it’s worth making sure that you have enough credit.

Should you go through these and not see any problems, it’s time to contact a Gas Safe registered engineer as there’s likely to be an issue within the unit.

Frozen condensate pipe (F1, F4, F28 or F29)

A condensate pipe on condensing boilers transports the acidic water, caused by waste gas, away from the boiler. This usually runs outside into a drain so in the colder months being outside can lead to it freezing over.

Thawing a frozen condensate pipe

Thawing out a frozen condensate pipe is something you can do yourself without the need for a fully-qualified heating engineer, in fact, you can find out how to do it using our guide to thawing a frozen condensate pipe. While this is something you can do yourself, don’t feel like you have to do it, if you feel the slightest bit unsure or unsafe, don’t hesitate to contact a Gas Safe registered engineer.

Gurgling, banging or whistling noises

Any strange noises you're hearing could be caused by a variety of things including air in the system, alternatively the water pressure could be too low or it's kettling. You might be able to determine the type of problem your boiler is having based on the type of noise it is making. Take a look at our guide to central heating noises to help you determine the cause of your noisy boiler.

PCB fault (F13)

The printed circuit board (PCB) is effectively the ‘brain’ of modern boilers as it sends and receives signals from all the electrical components within the unit. A faulty, broken or unconfigured PCB will prevent your Glow-worm boiler from working properly.

How to fix a faulty PCB

An issue with the PCB is commonly seen after a new one has been fitted due to the incorrect model being installed or it being unconfigured. In the case that one of these is the problem, a heating engineer will be able to safely replace or configure the PCB.

However, if the PCB is broken then a new one will have to be fitted, which can come at a fairly large expense, so you might want to consider a new boiler. Especially because an issue with the PCB can bring to light issue with other electrical components, such as the pump and fan.

Need a boiler repair?



Which Glow-worm boiler problems need an engineer?

Identify the possible cause of a fault with your boiler using the table below, it will also let you know if you'll need an engineer.

Problem Possible cause Do you need an engineer?
No heat or hot water Broken diaphragms and airlocks, failure of motorised valves, issues with the thermostat or low water levels Yes
Leaking and dripping Most common cause is a broken internal component but it will depend where the water is leaking from Yes
Banging, whistling or gurgling noises A common cause is air in the system, alternatively it could be that the water pressure is too low or it's kettling Yes
Pilot light goes out Could be a broken thermocouple which is stopping the gas supply Yes
Losing pressure There could be a water leak in the system, the pressure relief valve needs replacing or the radiators have been bled recently No unless there’s a leak
Frozen condensate pipe Your boiler should display a fault code or warning notification Yes
Thermostat issues Thermostat may be turned off or not set to the correct settings (time etc.) Consider replacing
Kettling Limescale or sludge building up on the boiler's heat exchanger Yes
Radiators not getting hot Sludge or air build up in the system or an unequal distribution of heat You will need to bleed the radiators which doesn't require an engineer unless you don't feel like carrying out the task yourself.
Boiler keeps switching itself off Could be low water pressure, a problem with the thermostat or a lack of water flow due to a closed valve, air in the system or the pump not circulating the water in the system correctly Yes

Glow-worm boiler warranty

Glow-worm boilers come with 2-7 years of warranty as standard but some models are eligible for up to 15 years of warranty through Glow-worm's club energy installers. Find out more with our guide to Glow-worm warranties. Keeping the warranty valid means arranging for an annual service of your Glow-worm boiler that will also ensure the safe and efficient running of the unit.

Boiler insurance and ongoing cover

If your boiler warranty has ended or will be coming to an end soon, it might be worth considering boiler insurance. This insurance can be taken out with your energy supplier, but there's absolutely no obligation to do so. When comparing boiler insurance, keep an eye out for ones that offer annual service and safety inspections.

Is it time to replace your Glow-worm boiler?

When you've had your Glow-worm boiler for a long period of time, you might be thinking about getting a new one installed. A brand new boiler could be saving you up to £300* a year if you live in a detached home. The table below shows how much you could be saving depending on your current boiler rating and property.

House Type G (less than 70%) F (70-74%) E (74-78%) D (78-82%)
Semi-detached £195 £140 £125 £110
Detached £300 £210 £165 £135
Detached bungalow £155 £110 £100 £90
Mid-terrace £170 £120 £105 £95
Mid-floor flat £80 £55 £50 £45

How to find the best boiler installers

If you're looking to replace your Glow-worm boiler then a Gas Safe registered engineer will be needed to carry out the installation. The decision you have to make is whether to go with a local engineer or national company.

With local engineers, you're likely to be offered a very competitive rate and they're likely to deliver a personal service throughout your communications.

National companies may cost slightly more but you'll have the safety of big brand protection and they could provide extra services such as ongoing boiler cover.

We recommend getting up to 3 quotes from different engineers when considering who should carry out any boiler-related work. Using our service you can get free quotes from reliable engineers near you.

*According to the latest figures from the Energy Saving Trust

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Rob Wells

About the author

Rob Wells

Rob is another of our resident home heating experts. He manages our external partnerships, making sure you get the most up to date information.

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