What is a Vaillant coding plug?How Vaillant uses coding plugs to enable appliance options
A Vaillant coding plug is a small resistor in a connector housing that tells a Vaillant appliance which option or configuration applies. The best-known example is the cooling coding plug. This page explains what coding plugs are and how the heat pump uses them.
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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. On start-up and during operation it reads the resistance on that input. A recognised value unlocks the matching behaviour — for example, permitting cooling mode to appear 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 — Vaillant part 0020266328, also supplied as 0020269259 — is the coding plug that authorises active cooling on compatible aroTHERM and VWL heat pumps. It is the single most asked-about Vaillant coding plug, because cooling is a popular retrofit.
Frequently asked questions
Is a coding plug the same as the cooling resistor?
The cooling resistor is one specific coding plug — the one that authorises cooling. "Coding plug" is the general term; "cooling resistor" or "cooling code plug" refers to the cooling one.
Does a coding plug need programming?
No. A coding plug is purely a resistor of a fixed value. There is nothing to program — the controller reads the value and applies the matching setting.
Can the setting be lost?
No. Because the configuration is physical — a resistor in a connector — it survives power cuts and software resets for as long as the plug stays fitted.