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Glow-worm Boiler Troubleshooting [Common Faults and Fixes]

Are you experiencing Glow-worm boiler problems? You’re not alone. Though it’s owned by the reputable Vaillant Group, Glow-worm is very much a “budget” boiler brand that’s known for frequent breakdowns.

The good news? Most of these faults are simple enough to repair. And in our guide below, we’ll walk you through the most common Glow-worm boiler fault codes, explain the issues they represent, and suggest possible fixes.

Glow-worm boiler problems

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Glow-worm Boiler Troubleshooting — Problems, Fault Codes, and Fixes

If you know which error code you’re dealing with, you can go ahead and jump to the right section using the links below.


Fault Codes

Gas Valve Control is Defective F14
Ignition or Fan Problems F1, F3, F4
Water Pressure Sensor Error F9
Flame Detection Fault (on 24/30CI models) F16
Main Circuit Board Connection Fault F11
Low Pressure F22
Betacom works sporadically F61-F67

Gas Valve Control is Defective — F14 Boiler Fault

One of the most common problems occurs with Glow-worm boilers from the Flexicom CX range. In particular, this affects the Flexicom CX 24 and Flexicom CX 30 models.

If you have a F14 error code showing on your boiler, there’s one thing you need to check — that the Printed Circuit Board (PCB) is getting power.

This component essentially powers and programs your boiler.

If you’re satisfied that there’s no PCB connection fault, 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 a Gas Safe boiler engineer) to try and fix it unless you have a boiler cover plan that includes these repair costs.

Fixing the F14 Fault

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

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

Ignition or Fan Problems — F1 Fault (Also F3 & F4)

Like the F14 fault code, we find the F1, F3 and F4 are common on the Glow-worm Flexicom CX 24 and 30. These fault codes aren’t 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 the F1, F3 and F4 Faults

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

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

However, if there are no connection faults, the next step is to test out the ignition leads. In the event that the problem lies here, the leads can simply be replaced. Usually, you can pick them up for less than £100, so it makes sense to replace just the leads rather than the whole boiler.

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Water Pressure Sensor Error — F9 Error Code

If there’s one Glow-worm boiler fault code we hate, it’s the F9. There’s a good reason for this. Even though it’s officially the “water pressure sensor error,” the code doesn’t actually point out any specific problem.

In fact, any of the problems below could trigger the fault:

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

Fixing the F9 Fault

This really is a fact-finding mission. What we’ve found with the F9 code, is that many affected boilers are running on a central heating 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, your engineer will be able to clear these blockages. If not, they’ll have no choice but to replace the affected part.

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

Flame Detection Fault (24CI/30CI) — F16 Error Code

If you have a 24CI or 30CI, you might have noticed a F16 fault code on the display. 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 clear the flame detection fault. 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.

Main Circuit Board Connection Fault — F11 Code on Display

The F11 Glow-Worm fault code will appear when there is a connection problem with the main circuit board. And typically, this is a heating temperature sensor fault, which directly relates to the flow and return thermistor.

Fixing the F11 Fault

Multimeters are a boiler breakdown engineer’s best friend. Gas Safe boiler engineers can usually fix the problem behind the F11 fault code by replacing the return (or flow) thermistor, so the boiler PCB can accurately detect the central heating return temperature range. However, there might be other intermittent issues, and checking connections using a multimeter can help show if this is the case.

Low Pressure — F22 Fault

The F22 error code signifies low pressure. If this has recently come onto the display and your boiler is losing pressure, there’s a good chance you have a boiler 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 definitely a leak somewhere. A visual check will usually pinpoint the leak, which you can easily fixed — as long as it’s not under the floor boards.

And if this doesn’t fix the problem, there’s a good chance that you’ve got air in the system — something you can resolve by bleeding all the radiators. Remember to bleed any towel rails, too, as these usually suffer from the most air build-up.

Betacom Works One Day, But Not The Next — F61-F67 Fault Codes

We’ve been called out to both Betacom 24Cs and Betacom 30Cs, where they work perfectly one day, but produce no heat or domestic hot water the next. In these cases, the boiler will typically show F61, F62, and F63 fault codes. However, fault codes F64 – F67 can point to the same problems.

In either event, the root cause usually lies in a faulty circuit, either 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 find the weak circuit.

If the fault doesn’t lie with the PCB, replacement parts should be easy enough to source, and 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.

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, buying a replacement boiler is the best option. You can get the likes of a Worcester Bosch with a 10-year warranty fitted for incredible prices with a range of finance options.

You can check prices for a new boiler on Heatable’s website. All you have to do is fill out an anonymous questionnaire about your heating system, and you’ll get a range of fixed-price boiler quotes.

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

FAQs About Glow-worm Boiler Faults

As we conclude, we’ll take a moment to answer questions that often come up about Glow-worm boilers and the problems they’re known to experience.

Why is my Glow-worm boiler not firing up?

There could be several reasons a boiler isn’t firing up, these include:

  • Ignition failure
  • Issue with the gas or electricity supply
  • Boiler has been locked out due to a safety issue, like a malfunctioning fan or a clogged condensate pipe

You may be able to diagnose some of these problems without professional assistance. For instance, if there’s been a power cut or your other gas appliances aren’t working, then your boiler is probably not getting gas or electricity and thus can’t switch on.

If you your boiler won’t fire up on a frigid winter day and there are no problems with the gas or power supply, you should check the boiler’s condensate pipe. If it’s frozen over, you can thaw it out with warm water, then reset your boiler to get it working again.

Now, if the boiler is locked out, you may be able to diagnose the problem based on the error code that’s displayed. That said, unless it’s a small enough problem like a clogged pipe that you can thaw yourself, you should always contact a Gas Safe registered engineer to assist you.

How do I reset my Glow-worm boiler?

Resetting a Glow-worm boiler is simple. All you need to do is press the reset button and hold it for 3-5 seconds (boiler manuals typically state where a particular model’s reset button is, and how long it needs to be pressed down). The boiler should then take several minutes to restart.

Note that you should only reset your appliance after fixing the issue behind the lockout, which is a safety switch-off procedure that shuts the boiler down when it isn’t safe to operate. This may mean that you’ll need a Gas Safe engineer to come in and inspect the boiler, repair or replace the faulty boiler component, and only then proceed with the reset procedure.

How do you adjust the pressure on a Glow-worm boiler?

It depends on the pressure issue. If the boiler pressure gauge is showing a reading that’s too low, there’s likely a leak somewhere in the heating system; you’ll have to repair the leaky component before topping up the boiler’s water levels via the filling loop. A pressure sensor fault could be another cause; you can learn more about low pressure problems in our guide here.

Conversely, if the pressure is too high, you’ll need to figure out why it keeps rising above the normal threshold and repair the underlying problem. You can read our guide to high boiler pressure here.

What’s Next?

Hopefully, our guide to some common Glow-worm issues has helped you understand what the fault is, and how it’s fixed.

If you have any questions, please get in touch by leaving a comment below.

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