F83 Vaillant boiler fault code

F83 Vaillant Boiler Fault Code: What You Can Check

Last updated on June 10th, 2024

The Vaillant boiler F83 fault code, and all Vaillant boiler fault codes, show on the display when there is a problem and your boiler locks out.

Vaillant uses them to show you what might be wrong with the boiler not firing up.

I have been a full-time boiler repairer for over a decade and having fault codes on the screen when I arrive is very welcome.

In this post, I’ll go through some of the reasons for your F83 fault and some potential fixes.

Vaillant boiler front badge

What Does F83 Mean on a Vaillant Boiler?

The cause of an F83 fault code on a Vaillant boiler is the boiler has been locked out due to dry fire.

An F83 fault code could also mean that a part on the boiler is broken and needs to be replaced.

Here is what the Vaillant Ecotec manual says about their F.83 Vaillant fault code:

What Does F83 Mean on a Vaillant Boiler
Vaillant F.83 meaning

How to Fix F83 Fault on a Vaillant Boiler

To fix the F83 fault code on your Vaillant boiler, the first things I would do is:

  1. Bleed any air out of the heating system and make sure the pressure is around 1.5 bar and reset the boiler
  2. Check wiring on and test thermistors
  3. Check gas rate and inlet pressure at the gas valve

Other Causes of F83 Vaillant Fault

How to check pressure on a Vaillant boiler

Low boiler pressure is the most common cause of a Vaillant boiler F83 fault code, but here are some other potential causes:

  • NTC thermistor is faulty: Flow or return temperature sensor can be out of calibration or not connected properly. This will need to be secured or replaced
  • Thermistor wiring damaged or loose: The wiring on the thermistors will need fully checked from thermistor to PCB for any damage or loose connections. Any problems will need fixed or replaced
  • Low heat input on heat exchanger: This can be caused a gas valve problem or lack of thermal transfer from the combustion chamber.

Vaillant F83 Fault Reset

The first thing I would do on a Vaillant boiler that is not working, no matter what fault code is showing, is to check the pressure and reset the boiler.

Vaillant boiler reset button
Vaillant boiler reset button

Knowing how to reset a Vaillant boiler is the simplest way to get your boiler working again, as it might have just locked out.

To reset a Vaillant boiler, you must find the reset button. This is usually a flame with a line through it.

You have to press the button to reset the boiler. Sometimes you have to hold it down for 3 seconds, but on some Vaillant boilers, it just needs to be pressed.

Vaillant Boiler Guides


A Vaillant F83 error on your boiler can sometimes be easily fixed without opening the boiler.

You should repressurise your Vaillant boiler and reset it as your first port of call.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

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1 thought on “F83 Vaillant Boiler Fault Code: What You Can Check”

  1. Dear Sir i have a Vaillant comby boiler etec plus 937 two days ago the hot water to the bath and sink upstairs slowed down to a trickle ,but the kitchen hot water was as normal , i had a plumber to look at it and he said the hot water pipe must be blocked up ,it can not ber the boiler because the kitchen tap is has normal fast rate. so today i disconected the hot pipe upstairs under the sink and connected the cold water pipe to the hot pipe and disconected the hot pipe downstairs and put a hose pipe to the outside and tuned the cold water on and that proved that tha hot water pipe was not blocked up , please help ,regards terry ,email [email protected]

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