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The Vaillant F28 boiler fault code relates to a lack of flame. On start-up, your boiler will attempt to fire up 3 times. If it's unable to do so, it will lockout and won't work again until the issue is fixed and the boiler is reset.
The F28 fault code is classed as a "lack of flame" or "flame not detected" = the boiler wasn’t able to create a flame.
This is different to a fault code that relates to "loss of flame" = the boiler had a flame, and now it doesn't.
This is a common issue on a range of Vaillant boilers, including the EcoTec and EcoFit.
You'll see the F28 fault code displayed on Saunier Duval boilers, as well as Glow-worm. This page applies to those brands too.
Glow-worm boilers were acquired by Vaillant in 2001, so most of Vaillant's / Glow-worm's fault codes are the same.
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So, we know that your Vaillant boiler shows the F28 fault code, due to a flame not being detected. But, what would cause a flame not to be detected in the first place?
Typically, this is due to a gas supply or ignition issue. It’s common if the boiler is old and has not been used for a while (they like to be used). It's also extremely common in cold weather.
There are two main things your Gas Safe repair engineer will need to focus on:
Whilst rare, it's not unheard of to have a faulty PCB.
The PCB in your Vaillant boiler controls all components. It receives signals from sensors and uses those signals to determine what other components should do.
As an example, if it receives a signal from the flame sensor that there is no flame, it will attempt to fire up 3 times before locking out. In this case, it then tells the display to show the F28 fault code.
The PCB needs to send an ignition signal, open the gas valve and then receive a signal that there is a flame. If the PCB is malfunctioning it may misinterpret signals (or not receive them at all).
So, your boiler could be operating correctly, but your PCB thinks it isn't.
If your Vaillant boiler needs a new PCB, expect the cost to be in the region of £500. At this point, you need to decide if spending £500+ on repairing an old boiler is worth it.
New boilers are incredibly efficient (energy bill savings) and come with a long warranty (5+ years).
With prices starting at £2,200, it's worth comparing installation cost using our new boiler quote tool directly with repair cost.
If you’ve not had problems with your boiler before and it’s locked out during one of the coldest days of the year, your condensate pipe could be to blame.
This pipe carries waste liquid from your boiler to prevent blockages. Unfortunately, if it’s not flowing fast enough and it’s cold enough outside, this waste can freeze. Your boiler senses a slight blockage and locks out displaying the F28 fault code.
Luckily, this is the quickest, easiest and cheapest fix. Simply pour warm water over the condensate pipe to thaw it out.
It’s important to use warm water so the condensate pipe doesn’t crack. And ensure you slowly pour it on the condensate pipe, not in it.
Once the condensate pipe is thawed out, resetting your Vaillant boiler should clear the F28 fault code.
If this doesn’t clear the fault code, it’s likely the issue is something else on this list, all of which require a Gas Safe repair engineer.
A lack of flame could indicate insufficient gas supply.
For those using a prepaid gas meter, the first thing to check is that there is sufficient credit.
After this, there are various checks that need to be made by a Gas Safe engineer.
This includes checking the gas isolation valve hasn't been turned off. This is usually turned off during maintenance. When it’s turned back on, air can be introduced to the system so your engineer will want to test this before moving onto the meter.
If there's not sufficient gas pressure into the meter, it's likely this is a utility issue. You'll need to contact your utility provider and inform them of the issue.
Generally, if there's a gas outage or issue in your local area, you won't be the only one affected. Utility companies are required to fix gas pressure issues (from the mains supply) for free.
For any boiler showing the F28 error code, an ignition component failure is high on the list of typical problems.
If your boiler can't create a spark, then it won't be able to produce a flame. Your Gas Safe engineer needs to inspect the ignition electrode and ignition lead. If these can't be cleaned or fixed, they'll need to be replaced.
A ball-park figure for this fix from a Gas Safe engineer is likely to be in the £250 range.
As we mentioned above, if the PCB is receiving the wrong or no signal from sensors due to it being faulty, it would need to be replaced.
However, before investing £500+ in a PCB replacement, it's worth checking out other potential culprits.
The flame sensor has one simple job; tell the PCB when there is a flame, and when there isn't. If the flame sensor is faulty, naturally, it's not going to be giving the PCB the correct signal.
Your Gas Safe engineer will be able to check the flame sensor visually and with a multi-meter to determine if it's faulty or not.
Whilst this isn't a free fix, it's not massively expensive. Depending on your exact boiler, a new flame sensor should be in the region of £150-£225, including parts and labour.
Without sufficient gas, your boiler won't ignite. We've mentioned one issue that would prevent your boiler from supplying sufficient gas (low pressure into the meter).
However, a more common fault on modern boilers (including Vaillant) is a stuck or broken gas valve. Alongside this, old age could mean it's had a full on electrical failure.
It's rarely worth paying an engineer (typically £50+ per hour labour) to spend hours trying to fix old components, as they're only likely to break down again in the future. Instead, a replacement gas valve is the way to go.
Once your engineer has confirmed that this is the issue, expect a replacement gas valve to cost £250-£350.
Of course, if you prefer, it's worth investigating whether replacing your boiler is going to be more cost efficient long-term.
You'll be covered by warranty, save money on gas bills, and get one fitted for as little as £2,300. Check prices using our boiler replacement quote tool here.
It means no flame detected. One of the causes could be low gas pressure due to a faulty valve, or low gas pressure from mains supply.
No, you shouldn’t use a boiler with any fault code displayed. Your boiler should lockout when a fault code is displayed.
The F28 error relates to no flame detected, but not necessarily no gas. It could be a flame detection issue, or low gas pressure.
A broken gas valve is likely to cost £250-£350 on most popular boilers such as Vaillant, Ideal and Worcester Bosch.
No flame detected. This is a reasonably generic code, as there are lots of reasons your boiler will lock out and not provide a flame such as issues with: circulation, gas pressure or ignition components.
A boiler engineer needs to fix the “no flame detected” error before resetting your boiler. Otherwise, the F28 fault code will still be present.
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