Glow Worm Boiler Faults [And What You Need To Do Next]

If your Glow-Worm boiler has a fault, you’ve come to the right place.

We are called out to boiler breakdowns daily. And, there are two brands that seem to be more intermittent than any others; Glow-Worm and Vokera. Which to be honest is strange, because Glow-Worm is actually part of Vaillant, and their boilers are known for being extremely reliable.

I suppose there is a good reason for this. Both Glow-Worm and Vokera are the budget of the budget boilers. They really are at the lower end in terms of performance and quality.

But don’t despair just yet. Many Glow-Worm faults can be fixed quickly and easily. Many times, a simple replacement component can be fitted and the problem is fixed, giving you an extra couple of years before you need a new boiler.

Hey, need someone to help fix the fault with your Glow-Worm boiler? You can find an engineer to offer a quote here.

Alternatively, you can get a fixed price online for a new boiler using Heatable’s 90-second quote form.

F14 Fault Code

One of the most common issues we find with Glow-Worm boilers is with the Flexicom CX range. In particular, the Flexicom CX 24 and Flexicom CX 30.

If you have a F14 fault code showing on your Glow-Worm, there’s one thing you need to check; that the Printed Circuit Board (PCB) is getting power. This is essentially what powers and programs your boiler.

If you’re happy that you do have power to the PCB, that’s good news. The PCB is extremely expensive to fix and in many cases, a new boiler is really the only option.

Now, it’s likely that the gas valve (this regulates the flow of gas to the boiler) is the issue. Sometimes, they can be fixed. Honestly? It’s really not worth spending time (and paying an engineer) to try and fix it.

Fixing an F14 Fault

Assuming the PCB is fine, the quick and easy fix for the F14 fault code is to have a Gas Safe engineer come out and replace the gas valve.

With repairs like this, you’ll want a general boiler health check. It doesn’t make sense to invest hundreds of pounds in a deteriorating boiler, when you can get one fitted from companies like Heatable and pay less than £20 per month; up to 10-years warranty will be included.

F1 Fault Code

Like the F14 fault code, we find the F1, F3 and F4 is common on the Glow-Worm Flexicom CX 24 and 30. This isn’t usually as simple as the F14, as a lot of the time, all codes will show all at once and this doesn’t help an engineer to determine the exact problem.

The problem can relate to:

  • Problems with the boiler igniting
  • Problems with the operation of the fan (usually, it’s running at the incorrect speed)

Fixing F1, F3 and F4 Faults

An engineer will usually start the diagnostic process by using a multimeter.

Using this tool, they will be able to determine if there are any week connections to the PCB, and from the PCB to the fan. If there is, this will cause intermittent problems.

If there are no issues here, the next step is to test out the ignition leads. If the fault lies here, they can simply be replaced. Usually, they can be picked up for less than £100, so it makes sense to replace just the leads, rather than the whole boiler.

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Betacom Works One Day, But Not The Next

We’ve been called out to both Glow-Worm Betacom 24C’s and Betacom 30C’s where they work perfectly one day, but not the next. Usually, the boiler will be showing a fault code of F61, F62 and F63. However, the same problems can occur when the fault code on the display is F64, F65 and finally F67.

Like the F1, F2 and F3 fault codes, this is usually related to a faulty circuit somewhere in the boiler. This could be with the PCB or ignition leads.

Fixing Betacom Faults

A multimeter is the best tool to determine where weak connections on an electrical circuit. An engineer will work through each component methodically to determine where the weak circuit is.

If the fault doesn’t lie with the PCB, usually replacement parts can be sourced and these replacements are much more economical than replacing the whole boiler.

It’s rare that we will replace a PCB. The simple reason is that they can cost up to £500 including installation. Especially with an older boiler that is likely to have other issues, it makes much more sense to replace the whole boiler unit. You can get an on-screen price for a replacement boiler here.

F9 Fault Code on Display Panel

If there’s one Glow-Worm boiler fault code we hate, it’s the F9. There’s a good reason for this; the code doesn’t point out any specific problem. In fact, the problem could be related to:

  • A diverter valve failure
  • Water or gas distribution (or flow)
  • Low or high boiler pressure
  • Faulty connections
  • Blocked heat exchanger

Fixing The F9 Boiler Fault

This really is a fact-finding mission. What we have found is that many Glow-Worm boilers having a F9 related problem are running on a system that has not been flushed, or doesn’t have adequate chemicals in it.

The particles circulating in the water find their way into expensive boiler parts like the heat exchanger and block them up. Sometimes, this can be cleaned. If not, it will have to be replaced.

On other occasions, we’ve found leaks in a system are causing low boiler pressure, or that using a multimeter, we were able to find a weak connection to the fan.

F16 Fault Code On Glow-Worm 24CI/30CI Boilers

If you have a 24CI or 30CI, you might have noticed a F16 fault code being displayed. Sometimes, the code can disappear by itself, but it’s likely it will return in a matter of days.

We’ve found with some breakdowns, that the gas assembly was faulty or blocked, meaning the boiler wasn’t getting enough gas to fire.

Usually though, the problem stems from the ignition leads and probe. These help the boiler fire and when they get blocked up, the boiler won’t work.

Fixing The F16 Fault Code

Replacing the gas assembly, ignition leads and probe will usually do the trick. But, make sure you get a qualified Gas Safe engineer out to analyse the situation. There’s no point replacing parts for the sake of it.

F11 Shown on Display

The F11 Glow-Worm fault code will be displayed when there is a connection problem with the main circuit board. And, this is usually directly related to the flow and return thermistor.

Fixing the F11 Fault

Multimeters are a boiler breakdown engineer’s best friend. The problem can usually be fixed by replacing either the flow or return thermistor. However, there might be other intermittent issues, and checking connections using a multimeter can help to show if this is the case.

F22 Fault Code, And Low Pressure

The F22 boiler fault code is directly related to low pressure. If this has recently come onto the display and your boiler is losing pressure, there’s a good chance you have a leak. Otherwise, there’s likely to be an air lock in the system.

Fixing the F22 Fault

If your boiler not only has low pressure but is losing pressure, there’s a leak somewhere. A visual check will usually highlight the leak, and leaks are easily fixed (if they are not under floors).

If that doesn’t fix the problem, there’s a good chance there is air in the system. Usually, and this can be fixed by bleeding all the radiators. Remember to bleed any towel rails too, as these usually have the most air build up.

Should You Fix Or Replace Your Glow-Worm Boiler?

The most cost effective solution, long-term, is the right one. Typically, when repairs exceed £500 and a boiler is out of warranty, a replacement boiler is the best option. You can get the likes of a Worcester Bosch with a 10-year warranty fitted for less than £1,795 per month, and even organise finance for less than £20 per month.

You can check prices for a new boiler on Heatable’s website.

For repairs under £500, especially when many parts are in good condition or under warranty, it makes more sense to repair the boiler, rather than replace it.

What’s Next?

Hopefully, uncovering some common Glow-Worm boiler problems has helped you understand what the fault is, and how it’s fixed. If you have any questions, please get in touch.

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  1. Glowworm HXI30
    Room stat calls for heat and boiler stat is set high say 70
    But boiler reaches 45 and switches off, drops to 43 and start up again and recycles like this never getting above 45.
    When hot water is called for it is not HOT, but just very warm.

    1. Hi Gill. F14 is flow temperature overheat. It could be an actual overheat, or a NTC thermistor that’s faulty and logging incorrect resistance readings. I’d call a Gas Safe engineer to figure out which is the case.

  2. Hi
    i have an old glow worn betacom 30c combi boiler. The heating and hot water are both doing the same thing when turned on.

    the pressure spikes from 1.5 to 3+ bar and then shuts off. if you leave them turned on they continue to do the same thing over and over.

    1. Hi Russ,

      This is likely to be a pressure release issue. To release pressure boilers use parts like expansion vessels, auto air-vents, pressure release valves and so on. If these don’t work well, you’ll get what you’re telling us. An engineer (see links in the article) should be able to give you an answer on what causes your 1.5 to 3+ bar spike.

  3. Hi.
    I have a Glow worm ultimate 30c combi natural gas boiler which was installed 23 march 2015 and has been annually serviced ever since.

    Its serial number is 21142800100153961300153953 N 8

    The control panel is not indicating a fault and appears to be working correctly.

    Domestic hot water is working fine so at that stage the flue exhaust fan presumably is working correctly and certainly sounds as is if it is.

    The central heating fires up and continues to run on low flame ONLY until it heats the home up.

    It is not bringing in main flame or the flue exhaust fan.

    So to an average home owner it may appear to be running o/k.

    however, I was a gas and oil combustion and commissioning engineer for many years so i know that the boiler has a problem.

    Is it possible you could throw some light on this situation.

    Kindest Regards


  4. I have f22 code on glow worm. I’ve read it’s to do with low pressure but how do you try and resolve it?

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