Vaillant error codes explained: what to do if your boiler breaks down

Is your Vaillant boiler not working? The first thing to do is to check the display on the boiler unit, which will display a unique code to identify the problem.

There’s a wide range of fault codes programmed into every Vaillant unit, but a select few crop up time and time again. Here are five common Vaillant fault codes – and what you can do to fix them.

Safety first!

Before you go opening up your boiler’s case and rooting around in the guts of your heating system, please remember that only Gas Safe registered engineers are legally qualified to carry out repairs on your domestic gas works.

Also, remember to ensure your house is safe – not just when your boiler is displaying a fault code, but at all times. If you smell gas, or if your carbon monoxide alarm is going off, immediately leave the building and call 0800 111 999. (If you haven’t got a carbon monoxide alarm, get one now!)

What does an F22 code mean?

An F22 code indicates an issue with low water pressure, which could mean:

  • the amount of water in your system is too low due to leaks, or
  • the pressure sensors inside your boiler system are faulty.

Every boiler needs water to heat up in order to operate – so if an F22 issue occurs, your boiler will go into a safety switch-off mode to prevent damage to the system. You’ll need to fix the issue before you can get your central heating switched on again.

How do I fix an F22 error?

If your boiler is displaying the F22 code, it’s best to get an engineer in to diagnose the exact cause of the drop in pressure. If there is a leak, you’ll need them to locate the source of the leak and fix it.

You can perform a quick fix using a filling loop while you’re waiting for your engineer to arrive – but be aware that this can cause further damage to your system if there is a bigger problem behind the scenes.

Some Vaillant boilers have an integrated filling loop, with the taps located on the bottom of the boiler unit. Other use an external filling loop (typically a flexible silver hose with valve taps at each end or just one end) which you’ll need attach to both the mains water outlet and the boiler intake. Look for two silver end caps – you’ll need to unscrew these and screw the filling loop onto each end.

Slowly open both valves and keep an eye on your boiler’s display or pressure gauge. Once you see a 1.3 to 1.5 bar pressure reading, close both taps and your system should be running again.

What does an F27 code mean?

An F27 indicates an issue with ‘flame detection’ – which essentially means the flame your boiler thinks it’s producing isn’t matching the amount of gas being used, or that the type of flame being produced isn’t correct (as least as far as the boiler’s sensors can tell).

There are a few potential causes for this:

  • the boiler’s electronic components are faulty due to moisture or dirt, or
  • the gas valve inside the boiler is leaking or stuck.

As with the F22 fault, an F27 issue will automatically shut off your boiler for safety reasons until the problem is fixed.

How do I fix an F27 error?

Unfortunately, unless you have Gas Safe certification, there’s nothing you can do to fix an F27 error. You should get an engineer to examine your central heating system as soon as possible.

The fault is often down to a faulty PCB (printed circuit board). If this is the case, and your boiler is already a bit long in the tooth, it’s usually cheaper to replace the whole boiler rather than replacing the PCB.

What does an F28 code mean?

An F28 code indicates an ignition failure within the boiler unit due to insufficient gas. There are a lot of potential causes for this, including:

  • problems with the gas valve within your boiler,
  • issues with gas supply elsewhere in your home,
  • condensate pipe or flue blockages,
  • a defective ignition electrode, or
  • faulty electronics.

How do I fix an F28 error?

  • If there’s no smell of gas and you’re confident that your home is safe, the first thing to check is your gas supply. Is it definitely switched on?
  • If the weather is cold, the condensate pipe may be frosted over – try pouring warm water over the condensate pipe to defrost it.
  • If your gas is definitely switched on and you’re not struggling through a cold snap, get a qualified engineer to check out the problem for you.

What does an F29 code mean?

The F29 error is very similar to the F28 error – it means the boiler did successfully ignite at one point, but the flame has subsequently gone back out during operation.

Many of the issues associated with F28 faults are also responsible for F29 faults; but rather than a lack of gas, it’s more likely that an external factor is affecting safe combustion.

How do I fix an F29 issue?

Follow the tips for an F28 issue above. Take extra care to check your house is safe, as an F29 problem can often be a lot more risky in terms of gas leaks.

What does an F75 code mean?

This is one of the most common issues that can strike down your central heating. Like the F22 error, it means that the system has detected a pressure discrepancy – but this is more likely down to:

  • a defective pump,
  • a blockage in your system,
  • a buildup of sludge or other contaminants on pressure sensors, or
  • an issue with the sensor itself.

How do I fix an F75 error?

As with many other boiler faults, fixing an F75 problem requires working with gas – and doing so without Gas Safe certification is a huge safety issue and a criminal offence. You won’t be able to fix the problem without the help of a qualified professional.

However, you can diagnose the cause of the problem yourself if you want to. Simply reset your boiler, turn on your heating or a hot tap, and listen out for the low rumble of your pump roughly every 20 seconds. If you can hear the pump, you’ll probably have an issue with your boiler’s sensors – if not, a broken pump is the more likely culprit.

Need an engineer to fix your central heating fault? As Vaillant Advance Installers, the team at Harrow Gas Services can quickly diagnose and fix all kinds of Vaillant boiler issues.

Call us on 07402 806032 to book an appointment with one of our Gas Safe registered engineers.