Last updated on October 28th, 2023
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.
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 (PDF) says about their F.83 Vaillant fault code:
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:
- Bleed any air out of the heating system and make sure the pressure is around 1.5 bar and reset the boiler
- Check wiring on and test thermistors
- Check gas rate and inlet pressure at the gas valve
Other Causes of F83 Vaillant Fault
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.
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.
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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.
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