Vokera Boiler A04 Fault Code


The Vokera fault code A04 boiler insufficient water pressure Q & A or require an engineer for an emergency boiler repair.


The Vokera Boiler Fault Code A04 Error Common Q&A


Just below, we have a list of common questions relating to the A04 fault code on the Vokera boiler.

Vokera Boiler A04 Fault Code Error

  • What does the A04 fault code mean on my Vokera boiler?
  • What is the correct pressure for my Vokera boiler?
  • Can I fix the A04 fault code on a DIY basis, or do I need a boiler engineer?
  • I’ve added water via the filling loop and now the pressure is too high, what should I do?
  • I top up my boiler, and within a few days/weeks the A04 fault code appears again, what is the problem?
  • Where do heating leaks come from?
  • I can’t find any leaks, so what is the problem?
  • I can see water dripping from my boiler, could this cause the A04 fault code to be displayed?
  • What could be leaking in my boiler and why?
  • My leaking boiler has been working intermittently since the A04 fault code was first displayed, why?
  • If the PCB is water damaged, can it be repaired?

What does the A04 fault code mean on my Vokera boiler?


When a Vokera boiler shows an A04 fault code on the display panel, it means that the system has insufficient water pressure.

For a boiler to work, the system needs to have enough water pressure.

If it has too much or too little it will lock out and display a fault code, in this case the A04.


What is the correct pressure for my Vokera boiler?


You should always refer to your owner’s manual for the correct water pressure for your boiler.

However, generally boilers will lock out when the pressure is above 3 bar, and below 1 bar.

The optimum working pressure for most modern boilers is 1.3 bar.


Can I fix the A04 fault code on a DIY basis, or do I need a boiler engineer?


There is a DIY fix to clear the A04 fault code.

Pressure can be topped up using the external filling loop. By opening this, you’ll be adding water and pressure to the system.

However, for the pressure in the boiler to be this low, it must have escaped.

So, whilst topping up pressure via the filling loop may clear the A04 fault code temporarily, it won’t fix the main problem at hand; pressure loss.


I’ve added water via the filling loop and now the pressure is too high, what should I do?


Firstly, make sure the heating and hot water is off. As the boiler heats up water, the system will increase in pressure slightly.

With the additional pressure already in the system, it could cause damage to internal boiler components.

A typical example would be the boiler’s pump seals. These are prone to blowing anyway, without the help of additional pressure.

The easiest way to release pressure on a DIY basis is to use a radiator bleed key to release air and water.

Slowly open the valve, making sure the floor is protected from dirty heating water, and you have a container to catch water.

Keep removing water until pressure drops to around 1.3 bar. If it drops below this, you can use the filling loop to top up the boiler again.


I top up my boiler, and within a few days/weeks the A04 fault code appears again, what is the problem?


As we mentioned, the A04 fault code is a quick fix to rectify the pressure problem. What it doesn’t do is fix the loss in pressure.

Loss in boiler pressure is usually due to a leak. As water escapes from the heating system, the pressure will drop.

And, that’s why we’d always suggest getting a heating engineer to have a look. This water is going somewhere.

It could be causing damage to your property, or to electronic components within the boiler.


Where do heating leaks come from?


Most leaks in a heating system are obvious.

Any part of the heating system that has water or moisture around it could be the source of the leak and cause the boiler to lose pressure and display the A04 fault code.

Examples of common places leaks can occur include:

  • Radiators, towels rails and their valves
  • Copper pipe work and soldered joints
  • A cracked heat exchanger
  • A leaking heating pump
  • Boiler connections, or loosely fitted magnetic system filters

Most of these leaks will be obvious, but some are harder to spot.

For instance, a pin hole in copper pipe work that’s set-in floorboards won’t be visible. It will only become obvious when damp patch appears on carpets or ceilings and by this point, it’s already caused considerable damage.


I can’t find any leaks, so what is the problem?


It’s quite rare, but there are other explanations whereby you wouldn’t see leaks from any of the above.

Typically, we’d head straight for the auto air vent and pressure release valve. If these units are faulty they could be leaking or allowing pressure to escape when they shouldn’t.

Failing that, the pressure gauge could be faulty. This will become obvious if you’re topping up your boiler with the external filling loop and the gauge isn’t moving. However, this is extremely uncommon.


I can see water dripping from my boiler, could this cause the A04 fault code to be displayed?


Any leak will contribute to pressure loss in your heating system, and this is likely the cause of your A04 fault code.

If you can see water dripping from your boiler then this is one of the most serious kinds of leaks.

What we find with boilers that leak, is the problem isn’t limited to the leak itself.

As the water drips, it makes its way into important boiler components. And sometimes, the water damage caused by these small leaks is enough to completely write a boiler off.


What could be leaking in my boiler and why?


As mentioned, if you suspect a leaky boiler, switch the heating and hot water off. This will help slow the leak and preserve any internal components.

The most likely causes of the leak would be the:

  • Heat exchanger
  • Pump

Heat exchangers in boilers are prone to cracking. And when they crack they’ll develop a small leak.

Unfortunately, it’s rare they can be repaired and instead they’ll need to be replaced. The cost of a replacement here could be in the region of £450-500.

Boiler pump leaks are usually cheaper to fix, as it’s the seals that are likely to be leaking. They could’ve blown due to high system pressure, or old age.

If the pump unit is in good condition, the seals can be replaced to fix the problem.

However, if the pump’s shaft and bearings are showing signs of excessive wear, it’s a much better idea to replace the whole unit. Expect to pay around £250 for a new pump to be installed.


My leaking boiler has been working intermittently since the A04 fault code was first displayed, why?


If you’ve topped up your boiler using the filling loop, and reset it to clear the A04 fault code, there’s a good chance you’ve left your boiler exposed.

The leak doesn’t suddenly stop just because a fault code is cleared.

We find that when there has been water damage and a boiler starts to work intermittently, it’s usually a case of a faulty printed circuit board (PCB).

The PCB is the heart of your Vokera boiler. If this has gotten water damaged due to the leak, then the whole boiler will start to malfunction. This is because the signals that the PCB gives and receives may not be incorrect.


If the PCB is water damaged, can it be repaired?


The PCB can be repaired if the work needed is minor. If not, a replacement could be £400-£500.

However, the problem we have here is:

  • There is a leak to fix (which is likely to be the pump or heat exchanger)
  • The PCB needs repairing or replacing

The repairs mentioned above could cost £600-£1,000 in total. And that doesn’t include the fact that the leak could have caused minor damage to other parts such as the gas valve and fan.

So, it’s important to have your heating engineer inspect all the electrical components in the boiler. If the PCB has gone, it’s likely other parts are going to break soon too.

There’s little point investing this kind of money in an old boiler, when a replacement will be more efficient and have a warranty of up to 10 years.

Other Vokera boiler issues


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