What is a Vaillant coding plug?

What a coding plug is

A coding plug is a connector that contains a resistor of a specific value. When it is plugged into a defined point in the appliance wiring, the controller measures the resistance and uses it as a setting. Different resistance values mean different configurations.

It is a simple, robust way to configure hardware: there is nothing to program, and the setting cannot be lost in a power cut or a software reset.

How the controller reads it

The heat pump controller has an input expecting a coding plug. It reads the resistance on that input, and a recognised value unlocks the matching behaviour — for example, making cooling available in the installer menu.

If no plug, or the wrong plug, is fitted, the controller simply does not offer the option.

The cooling coding plug

The cooling coding plug is the one that authorises active cooling on compatible aroTHERM Plus heat pumps. Vaillant sells it boxed as part 0020269259, labelled “Coding plug, cooling function”. The same blue plug is also sold in a Vaillant small-parts bag as part 0020266328.

Because Vaillant uses coding plugs for other options too, a plug of a similar shape is not necessarily the cooling one — always check the part number on the packaging.

Frequently asked questions