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Need help with a faulty Glow-worm boiler?

We depend so much on our boilers day in and day out, so it’s easy to forget that they’re even there, just doing their jobs – that is, until they break down and you’re left in the cold with no hot water or heating!

I know how stressful it is – I’ve been helping people in the Edinburgh area deal with faulty boilers for over 20 years, and I’ve had many a run-in with Glow-worm boilers in that time.

That’s why I thought I’d put together this handy blog post, to help you diagnose the problem and determine whether or not you need to call in an expert – as well as to give you an idea of how involved the fix will be!

NOTE: It’s important you DO NOT try to fix the problem yourself, unless it’s a very simple fix such as topping up water pressure or defrosting a frozen condensate pipe – for everything else, always call a Gas Safe registered engineer.

About Glow-worm boilers

Glow-worm is part of the Vaillant Group, and the company has its own dedicated service engineers to cover both Glow-worm and Vaillant boilers. Parts are easily available and reasonably priced, and they are a popular option for many of my clients.

The good news is that although Glow-worm is a budget boiler, it’s NOT a boiler brand with numerous faults and a bad reputation. The parts are usually easy enough to source, and from my experience you can usually replace just one part and the boiler will fire back up – unlike some other budget brands with simultaneous faults.

So, without further ado, let’s dive right into some of the most common Glow-worm faults and fixes

1. Fault code F16 (Ci models)

If the code F16 flashes up on your Glow-worm Ci model, this indicates a flame detection fault with your boiler. It could very well be that the boiler itself requires a service, and the probe needs cleaned or replaced. Please note though, I’ve also seen this code when the boiler is not igniting due to no gas coming through the pilot assembly,

The Fix: Check the pilot assembly is clean and free flowing from the gas valve. If so, replace the flame detection probe and lead.

2. Fault code F9

Next is the dreaded F9 code. The main problem here is that it’s a very generic code which can point to a few different faults relating to pressure, circulation and diverter valve issues. First, check your pump is running, then check all electrics from the circuit board. Is the boiler going through the correct sequence?

In my own personal experience, and usually also with communication from Glow-worm, this fault code has actually been caused by a sludged up plate heat exchanger – this can happen when the system has not been cleansed or adequately flushed.

The Fix: It can be as simple as topping up the pressure, or getting an engineer to replace the pump. However, as I mentioned above, I’ve found Glow-worm boilers are very sensitive to sludge build-up, so flushing the system may be advised.

TIP: Whenever I do this for my clients, I usually fit a magnetic filter and on one occasion, I’ve also replaced the thermistors (in the case of black iron oxide coating the sensors) – all good, and no second call-backs.

3. Fault codes F1, F3 & F4 (Flexicom CX range)

Codes F1 and F4 indicate an ignition fault, however F3 is a fan speed fault. However, if the fan does not come up to speed, you have an ignition fault, anyway. I’d recommend getting a multimeter out and checking your readings from the PCB to the fan. Also, check ignition leads and power from the PCB.

The Fix: An engineer will either replace the fan or the PCB. You may also need to replace the ignition leads, depending on the results you find from the multimeter readings.

4. Fault code F14 (Flexicom CX range)

If you were to look at the service manual, you’d find this fault states there’s a defective gas valve. However, check there is power from the PCB to the gas valve. If not, it’s not the gas valve at all, but either the PCB or the wiring harness.

The Fix: An engineer will likely either replace the gas valve or the PCB/wiring harness.

5. Fault codes F61, 62, 63, 64, 65, 67 (Betacom)

This is quite a range of faults with the Betacom models, however, all of these faults indicate there’s a problem with the main circuit board, or PCB. Before replacing the board, I would test the whole sequence with a multimeter. It could be a faulty connection from one of the components to the board, or the wiring harness.

When servicing a boiler, it’s not uncommon for a cable to get caught in the casing when putting back together, and this can cause a short circuit indicating a fault at the PCB.

The Fix: If there’s no joy after checking the sequence and connections, an engineer can replace your PCB to get things working again.

Conclusion

There we have it! Five common faults with a Glow-worm boiler. Luckily, Glow-worm is quite a reliable brand, and with parts easily available, it’s usually worth it to pay for repairs – unless you have a particularly old model.

I hope this blog post has given you a better idea of what might be causing the problem with your faulty Glow-worm boiler, but if not, please feel free to either leave a comment below or get in touch directly. I’ll be happy to help!