Are you looking for help with your faulty Vaillant boiler?

Dealing with a faulty boiler can be stressful, especially when you have to decipher fault codes and are left feeling unsure of what the problem actually is. Over the past few years, I’ve dealt with many Vaillant boilers and know most of their faults inside-out, which is why I decided to write this blog post to help you out.

Below are five of the most common faults and fixes you can try for your faulty Vaillant boiler, either yourself or with your local Gas Safe registered engineer.

TIP: If you’re in any doubt, or it’s not an easy fix such as low pressure or a frozen condensate, DO NOT try to fix the boiler yourself – always call a professional Gas Safe registered heating engineer.

About Vaillant boilers

The original inventor of the combi boiler, Vaillant has been at the forefront of German heating and engineering excellence for the past few decades. Well-known for manufacturing boilers that last the distance, they’ve also won an award for making the quietest boiler on the market, so great for installing in bedrooms.

Vaillant has their own dedicated service engineers, and more recently have made a large investment in Scotland by building a dedicated training centre.

Common fault 1: Code F22

If you see the code F22 show up in your display, a quick check of the manual will say something alone the lines of ‘dry fire, insufficient water’. This indicates your water pressure is low, which happens to be probably the most common boiler fault of all.

The Fix: This is an easy fix for most boilers with an external filling loop; simply open the little tap around a quarter turn until the display on the unit hits 1.5 bar, then close the tap again. You may have to reset the boiler. However, for Vaillant EcoTEC Plus models, it’s a little different, as they use a built-in filling loop.

For EcoTEC Plus models, look below the boiler; there should be two grey levers which will have ‘closed’ written on them – each should be sitting at the ‘quarter to 3’ position (if it were a clock). Open both of these valves a quarter turn, so you won’t be able to read ‘closed’ – they should now be at the 12:30 position.

Once the pressure returns to 1.5 bar, close the levers and reset the boiler.

Common Fault 2: Code F75

If the code F75 is flashing in your display, the fault is most likely to do with the boiler’s sensor not being aware that the pump has started running – so failing to notice a change in pressure. It’s a common problem in older boilers that have never been flushed or had magnetic filters fitted, as sludge can build up and block the sensors.

The Fix: The easiest solution here is to simply replace the sensor.

Common Fault 3: Codes F27 & F28

These codes refer to a frozen condensate pipe, meaning the condensate waste cannot run to the drain and is trapped in the boiler, causing the boiler to lock out.

The Fix: You may have to wait for the condensate to defrost. If the pipe runs outside, pour hot water over the pipe to defrost it, or place a bucket under the boiler and disconnect the plastic waste pipe on the far right of the boiler, before draining the condensate into the bucket.

Common Fault 4: Code F28 (Vaillant Turbomax)

This fault, particularly common for the Vaillant Turbomax, is caused by a faulty ignition, or no gas getting to the boiler.

The Fix: Firstly, check the condition of the ignition leads – is a spark being generated? If not, you should replace the ignition leads as this may fix the problem. If there is a spark, check the power to the gas valve and see if gas is flowing through. If there is power to the valve, but no gas flowing, it may need replaced.

Common Fault 5: Code F29

If the code F29 flashes up, the manual will probably tell you something along the lines of ‘flame extinguished’.

The Fix: If boiler is igniting, and then shutting off, check the flame sensors, flues and airways. You may have to replace the sensors, and the seals on your flue. Check your flue, extensions and bends are connected properly and have not come apart.


I hope you’ve found this blog useful when troubleshooting your faulty Vaillant boiler, but remember, unless it’s an easy fix such as low water pressure or a frozen condensate, it’s best to call in an registered Gas Safe registered engineer who has experience dealing with Vaillant boilers.

If you have any questions or are currently experiencing problems with your Vaillant boiler, please don’t hesitate to get in touch with me directly or drop me a comment – I’ll be happy to help!