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The Top 8 Boiler Fan Faults and Replacement Costs

This guide to boiler fan faults will take you through how boiler fans work and how to fix them when they stop working. In our research we’ve identified the top 8 most common faults, and what are replacement and repair costs for them.

How Boiler Fans Work

Boiler fans do not cool down the components inside a boiler. As fuel (gas, LPG, oil) burns in the combustion chamber, harmful gases are released.

Each boiler is fitted with a flue – this is a large white pipe that’s fitted to the boiler. You’ll either have a vertical flue (going through a roof) or a horizontal flue (going through a wall). This is what takes harmful gases away from your property.

However, the flue isn’t able to take away the gases from the boiler on its own, it’s simply a place for them to escape.

That’s where your boiler’s fan comes in. The fan creates a small draught that will push flue gases up and out of the flue.

The boiler fan will start up before anything else.

The printed circuit board (PCB) needs to recognise the fan is running before it fires up. If it doesn’t recognise the fan is running, it will lock out and display a fault code related to an air fault, or fan problem. Examples might be the Vaillant F32, Baxi 160 and Worcester C6 & C6.

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Boiler Fan Replacement Costs

Boiler fan replacement costs vary for one simple reason; no two boiler fans are the same price.

For instance, a Worcester Junior 28I fan is less than £100. On the flip side, a fan for a Baxi Solo 3 is nearly £200.

As a guideline, expect to pay in the region of £225-275 including parts and installation.

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Boiler Fan Repair Costs

Due to the price of labour, boiler fan repair costs are similar to replacement costs.

For that reason, unless the fix is an incredibly quick and simple one, we’d be looking for a replacement fan that’s going to last, rather than a repair.

Top Boiler Fan Faults

There are two types of faults to look out for:

  • Faults relating directly to the fan’s operation
  • Air faults, that hinder the fan’s operation

Let’s start with fan faults.

#1 – Fan Speed Too Low

A lot of homeowners have problems with their pilot light going out, or the boiler locking out shortly after ignition.

We’ve been asked if wind can create a big enough draft to blow out the pilot light and cause this fault.

That’s usually not the case, unless the fan speed is too low.

The draught the fan creates into the flue, should counter any draught trying to get into the flue (i.e. wind).

The Fix

Fingers crossed this is a fan speed issue, not a faulty boiler fan.

If this is the case, a Gas Safe engineer will be able to adjust the fan speed and reset the boiler.

#2 – Loose Wiring/Connections

Any noise stems from vibration. And those vibrations (over years) can cause the connections and wiring to work loose.

As we’ve mentioned the PCB needs to see a signal showing the fan is working.

If loose wiring or connections aren’t allowing that to happen, the boiler will lock out.

The Fix

Get a Gas Safe engineer to inspect the fan for loose wiring and connections. They’ll need to be secured.

While the boiler casing is off, it’s worthwhile asking the engineer to check all other connections.

Fans are robust components, so it’s likely other components are going to be suffering the same problem.

#3 – Damaged Wiring & Connections

Like loose connections, damaged wiring and connections are going to cause signal issues.

Typically, we find damage comes from boiler leaks, rather than from old age. And plenty of parts in a boiler are prone to leaking.

It could be something as simple as a loose connection, blown pump seal or on a more serious note – a cracked heat exchanger.

The Fix

First, a Gas Safe engineer needs to find and fix the leak.

Then, they’ll need to check if the damage is limited to the fan.

If it is, replacing damaged wiring and connections will fix the problem and clear the boiler fault code, ready for a reset.

#4 – Faulty Unit

If your boiler is 5+ years old, there’s a small chance the boiler’s fan has failed completely.

Most manufacturers (Wilo, Grundfos etc) will offer a service and repair kit for their fans.

However, there’s little point spending the time and money fixing a dodgy old fan.

The Fix

In this case, we’d suggest having a Gas Safe engineer replace the boiler’s fan.

For old boilers that are out of warranty, a better option might be to get a price for a new boiler. You can get prices using this form, in less than 90 seconds (prices are displayed on screen).

Top Air Faults That Affect A Fan’s Operation

The fault code system on boilers isn’t particularly complex.

Air faults can often be confused with fan faults, and vice-versa.

So, before writing the fan off it’s worth considering the following problems.

#1 – Flue Blockage

A blockage in the flue means harmful gases can’t escape. 

The boiler notices an increase in air pressure (as the fan continuously pushes harmful gases up the flue, and they don’t escape), and will shut down.

This is rare. But, if this is the case the cause could be:

  • A blockage in a vertical flue that doesn’t have a flue guard
  • A flue that has broken apart and is blocking itself

The Fix

It’s most likely the issue is with a vertical flue that doesn’t have a flue guard fitted.

Your engineer will need to inspect the flue, remove any debris and fit a flue guard so that debris can’t enter again.

If the flue has broken a part and blocked itself, it will need to be replaced.

#2 – Condensate Blockage

Condensate pipes vent harmful vapours from your boiler.

Unfortunately, they are prone to freezing in winter. That causes a blockage and an air pressure fluctuation as would happen with a flue blockage.

The Fix

The condensate pipe needs to be thawed out, as it’s likely the vapours have frozen.

Once you’ve thawed out the pipe, the pipe needs to be insulated using lagging.

If you’re in a particularly cold part of the UK, ArmourFlex lagging will provide that little bit more protection than traditional lagging.

#3 – Air Pressure Switch

We’ve mentioned that the boiler needs to know the fan is running and that there’s not a blockage, before it fires up.

It’s the air pressure switch that monitors air pressure in the boiler and determines if the boiler is safe to fire up, and to continue running.

The Fix

Assuming there’s no blockage or fault with your boiler fan, it’s likely the air pressure switch needs replacing.

#4 – Faulty PCB

If all other options have been exhausted, the PCB could be to blame.

This gives and receives signals to parts in the boiler, including the fan.

If the PCB isn’t working, it won’t receive the correct signals. So, it might think the boiler fan isn’t working, even when it is.

The Fix

The PCB can be tested using a multi-meter. Hopefully, it’s a simple case of loose connections.

If it’s not and the PCB is faulty, a replacement will be needed.

It’s a rare scenario when we replace a PCB.

They can cost more than £500, and we’d usually advise investing that in a brand new boiler with a long warranty.

What’s Next?

Thanks for reading our 3-minute guide to boiler fans.

Have other problems with your boiler? Check out our boiler fault finding guide.

Got boiler fan problems that haven’t been mentioned?

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  1. I had a boiler fan issue, fan pcb had burned out, so I replaced the whole fan unit, the boiler fired up and ran for about an two hours HW and CH, then it stopped, turns out the fan PCB had burnt out again.
    Is there any known issue causing this?

  2. Have used many registered engineers giving them access to buildings and most can not explain faults or operations of a boiler your site is excellent

  3. Hi, thanks for sharing. My Vaillant shows error with the fan but the fan does work (rotating) and air is going out from the flue. any idea what can be?

  4. Why won’t my ideal combi logic 30 boiler fan turn off after the electricity was turned off and then on again…just keeps running

  5. Hi, hope you can advise- when our boiler has become faulty, it started to heat radiators altogether with taps on any settings the plumber came and fixed that but he the boiler fan started to be on 24/7 and the burner comes on for few seconds every 10 min, its noisy especially in the evening in our open plan living room/ kitchen can’t hear TV, it never was like that- the plumber said there is nothing he can do – it’s old boiler- MAIN Combi 24HE, ser no. BML104550169AC.
    Kind regards

  6. I have a Glow-worm Micron 40 FF Boiler its telling me I have a Simultaneous Light Sequence-Fan/APS Fault.
    I have put the control knob to 0 put power on at isolation switch, I turn the control knob clock wise the fan starts up then 10 seconds later the boiler fires up.
    The boiler runs for about 15 minutes then stops telling me the fault I mentioned above.
    Can anyone advise it would be really appreciated.

  7. I have an uncommon fault. My Ideal Logic Heat 12 boiler keeps starting, running and stopping again randomly throughout the day and night without any ignition and without any demand for heat (shows 0), in a similar behaviour to post ignition run-on mode. The central heating and hot water systems are running normally in response to the thermostats/timers with normal indications on the boiler. Therefore the usual continuous running culprit of zone valves seem to be an unlikely cause. There is no indication of frost protection when the boiler misbehaves and the thermostats are set to higher than the 5 degrees frost setting anyway. Both telephone calls to the Ideal engineers and a local callout engineer have failed to diagnose the fault. The local engineer mentioned that his multimeter showed 50 volts on a boiler terminal which he expected to show zero, but did not know how to trace the source. I would prefer not to have to call out an Ideal engineer at £289 for a one time call out, and local repairers may well also prove as helpful/costly as the one already stumped. any thoughts?

  8. Have a Potterton suprima 50 boiler. About one a month the boiler starts to make loud droning noises which stop once the boiler is turned off. Boiler is c.20 years old and changing the pcb makes no difference. Please tell me the fan is dying as i did buy a brand new one few months ago which was never fitted to the boiler. Is this a job i could do myself?

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