Glow-Worm Boiler F3 Fault Code

The Glow-Worm fault code F3 relates to a fan fault and here we have Q & A or require an engineer for an emergency boiler repair.

The Glow-Worm Boiler Fault Code F3 Error Common Q & A

Just below, we have a list of common questions relating to the F1 fault code on the Glow-Worm Boiler.

What does the F3 fault code mean on my Glow-Worm boiler?
If there’s a fan fault, why won’t my boiler ignite?
Why is it that the PCB that needs to recognise the fan being operational, before the boiler ignites?
Will resetting my boiler fix the F3 fault code?
What could be wrong with my fan that causes the F3 fault code to be shown on the display panel?
Can a fan with a damaged shaft or bearings be fixed?
Is it likely that the fan speed has been set incorrectly?
It sounds unlikely that wiring and connections could be the cause of the problem, how can they contribute to the F3 fault code being displayed?
My boiler engineer thinks the fan needs replacing, how much is this going to cost?
What other things could contribute to the F3 fault code being displayed on my Glow-Worm boiler?
My boiler engineer thinks the PCB is to blame, is this possible?

What does the F3 fault code mean on my Glow-Worm boiler

Your Glow-Worm boiler has a function incorporated into it that detects when there is a problem. When a problem is detected, typically, the boiler will lock out. In some cases, this is to protect the boiler, where continued operation would damage internal components.

However, in the case of the F3 fault code on Glow-Worm boilers, it’s likely the lock out occurs, to stop the boiler from being dangerous.

The F3 code relates to a fan fault. The fan can’t reach the correct speed for the boiler to ignite.

If there’s a fan fault, why won’t my boiler ignite

The fan on your Glow-Worm boiler helps to vent harmful flue gases out of the flue. If these gases aren’t vented from your boiler, the appliance becomes dangerous.

For this reason, a boiler won’t ignite, until the printed circuit board recognises that the fan is operational. But, it doesn’t just need to be operational, it needs to be running at a speed that’s fast enough to vent these harmful gases.

Why is it that the PCB that needs to recognise the fan being operational, before the boiler ignites

Your boiler’s PCB is the heart of the operation. It monitors signals from a range of sensors and electrical components. Based on these signals, it knows which instructions it needs to send to which components.

For instance, when the fan starts up, the air pressure switch notices a change in air pressure. It feeds back to the PCB that the boiler is safe to ignite. In turn, the PCB tells the gas valve to open to supply gas to the burner, and the spark generator to produce a spark so that the burner ignites.

Likewise, when it doesn’t see components doing what they should be doing, it will lock out. In the case of the F3 fault code on your Glow-Worm boiler, the fan speed is too slow, or non-existent.

Will resetting my boiler fix the F3 fault code

It’s important to understand why you shouldn’t reset your boiler. First, a lock out is designed to signify that there’s a serious, and potentially dangerous problem. Resetting the boiler isn’t a function that’s designed to fix a boiler. It’s designed to be used after a Gas Safe engineer has fixed the problem.

Particularly on older boilers, that aren’t as complex, a reset might trick the boiler into working, maybe just for a few minutes. But, for the few minutes it does work before it locks out again, flue gases aren’t escaping via the flue, and that’s going to be dangerous.

So, don’t try and reset your boiler. Call a Gas Safe engineer to come and find the fault, fix it, and let them reset the boiler on your behalf.

What could be wrong with my fan that causes the F3 fault code to be shown on the display panel

Luckily, this fault is specific, in that your boiler engineer knows the problem is with the fan, or any component that works alongside it.

With the fan, your boiler engineer will need to check:

The shaft and bearings are in good condition
Fan speed is set correctly
Wiring and connections to the fan are not damaged or loose
The fan isn’t completely faulty

But, as good as fault code systems on boilers are, they’re not an exact science. If none of the above seems to be the issue, the problem could lie with a range of other components:

Flue (blockage)
Condensate (blockage)
Air pressure switch (incorrect signals being given)
PCB (incorrect signals being received or given)

As you can see, this problem isn’t as simple as replacing the fan, on many occasions.

Can a fan with a damaged shaft or bearings be fixed

Your Gas Safe repair company will be able to inspect the condition of the fan and determine whether it should be fixed or replaced. Any component can be reconditioned, but sometimes it makes sense to replace a tired and worn unit, rather than spending 100s on repair bills.

If the rest of the fan is in perfect condition, your boiler engineer will likely replace the shaft and bearings. As these components wear, it becomes harder and harder for the fan to turn. Eventually, that’s going to lead to the fan spinning slower than it should, not venting harmful flue gases, and the boiler locking out whilst displaying the F3 fault code.

Is it likely that the fan speed has been set incorrectly

It’s unlikely that fan speed has been set incorrectly. That is, unless the boiler is new (i.e. it came like that from the factory), or the fan has been replaced recently and the fan speed from the OEM manufacturer was incorrect.

Your boiler engineer will be able to check and test the fan speed and adjust if necessary. If the fan speed is incorrect, your boiler repair company will be able to test it, change it, and reset your boiler to clear the F3 fault code.

It sounds unlikely that wiring and connections could be the cause of the problem, how can they contribute to the F3 fault code being displayed

It’s a lot more common for wiring and connections to be the root cause of the problem than you might think.

There are two ways that wiring and connections can become damaged. And when they do, that’s going to lead to intermittent signals being passed between the PCB and the fan, incorrect fan speed, or the fan not operating at all.

Typically, we find it’s one of two things that has caused the problem.

The first, is boiler vibrations, working connections loose. This tends to happen on older boilers, where a part has failed. For instance, if the bearings were to fail on the pump, that’s going to mean that the pump isn’t operating smoothly and vibrates sporadically. This is enough to loosen connections to a point where signals aren’t being passed to and from the fan correctly.

Assuming there’s no long-term damage, the simple fix is to secure the connections to the fan. However, your boiler engineer will also need to fix the problem with the pump, by replacing that component, or the bearings. If they don’t, the same problem is going to happen again soon.

Another common problem is water damage. Again, we’ll use the pump as an example, although other parts can leak. The seals on the pump are fragile, they can degrade or be put under too much pressure over time and cause a leak. If this moisture finds its way onto the fans electronics, that’s going to cause issues.

Like the vibration-based issue, it’s not just the fan that needs to be fixed, the leak needs to be fixed too. The problem with leaks is once they start, they can cause a whole host of problems, with all electronics components in your boiler.

So, if you see water pooling below your boiler and see the F3 fault code on the display panel, call a Gas Safe engineer as soon as possible.

My boiler engineer thinks the fan needs replacing, how much is this going to cost

Not all problems with your boiler’s fan can be fixed or are worth fixing. If the cost of a repair is going to be close to the cost of a replacement, it makes much more sense to replace the fan.

Typically, you should expect to pay somewhere in the region of £250 for a replacement fan on your Glow-Worm boiler.

What other things could contribute to the F3 fault code being displayed on my Glow-Worm boiler

With all potential fan faults ruled out, the next step is to check for faults with anything that relates to airways on your boiler. Without the boiler sensing that all airways are free, and the fan is running, it won’t fire up.

This includes both the flue and condensate pipe. The flue lets dangerous gases escape, whereas as the flue allows condensed gases escape from the boiler. So, your boiler engineer will need to check that both airways aren’t blocked. A partial blockage in either of these pipes is going to lead to the boiler locking out, and a fault code like the F3 being displayed.

But, if these aren’t blocked, it’s worth having your boiler engineer check the air pressure switch. It’s this sensor that determines if there are any airway blockages. So, if it’s faulty, it could be reading a blockage, even when one isn’t present. A faulty air pressure switch could be the problem.

My boiler engineer thinks the PCB is to blame, is this possible

With almost any fault code, the PCB needs to be ruled out. It’s this component that gives and receives signals to all the important components in your boiler. More importantly, it’s the PCB that determines which fault code needs to be displayed. So, if the PCB is damaged, then the fault codes being displayed, could be completely wrong in the first place.

The first step is for your boiler engineer to check that the wires and connections are secure, and that there are no signs of water damage. After testing for power, they’ll be able to determine whether your PCB is getting power.

If the PCB isn’t getting power and needs replacing, you should expect to pay around £350-450.

Other Glow Worm boiler issues

For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.

We have more related issues with fan faults.

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