All Vaillant error codes
This page brings together Vaillant error codes sorted by type of fault: what each code means, its likely causes, and what you can safely check before calling a professional.
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The Vaillant codes on this page, grouped by type of fault.
Temperature sensor — Vaillant
These codes indicate a sensor that’s no longer returning a consistent value. The problem almost always comes from the sensor itself or its connector, rarely from the unit.
Code F42Medium severityair-to-water
Coding resistor fault
Possible causes
- Coding resistor missing or faulty
- Coding connector not properly plugged in
- Faulty circuit board
Models affected: aroTHERM, aroTHERM plus
This fault requires a qualified technician. Do not open the unit.
All Vaillant codes published on the site
This list updates automatically whenever a new guide is added.
Technical information provided for guidance only, based on manufacturer documentation and field reports. It does not replace the diagnosis of a qualified professional. Found an error on this page? Report it.