What is a Vaillant cooling resistor?The code plug that authorises cooling on aroTHERM & VWL heat pumps
The Vaillant cooling resistor is a small coding component — often called a "code plug" — that tells a Vaillant aroTHERM or VWL heat pump it is permitted to run in cooling mode. Without it fitted, the heat pump operates in heating and hot-water mode only. This page explains what it is, why a heat pump needs one, and what it does not do.
Updated
The short answer
The Vaillant cooling resistor is a coding plug that unlocks the cooling option on a compatible Vaillant heat pump. The heat pump controller reads the resistor and, only when it is present, exposes the cooling settings to the installer.
Vaillant supplies the part under number 0020266328, and under the functionally identical number 0020269259. The two are interchangeable.
Why a heat pump needs a resistor to cool
A Vaillant aroTHERM or VWL heat pump is physically capable of running its refrigerant cycle in reverse — removing heat from your home instead of adding it. The hardware to cool is already inside the unit.
Vaillant ships these heat pumps configured for heating and hot water only. Cooling is treated as a deliberately enabled option. The coding resistor is the physical token that unlocks it, so cooling is only ever commissioned on purpose, by a competent installer.
What the part physically is
It is a small resistor inside a plug-style connector housing — which is why installers call it a code plug. It fits a defined position in the heat pump wiring. The controller reads the resistor’s value; the correct value is the signal that means cooling is permitted.
What the resistor does — and what it does not do
The resistor does
Authorise the heat pump firmware to permit cooling mode. Without it fitted, cooling cannot be enabled in the installer menu at all.
The resistor does not
Switch cooling on by itself. After it is fitted, an installer must still enable cooling in the settings, and the heating system must be suitable for cooling.
Frequently asked questions
Is the cooling resistor the same as a code plug?
Yes. "Code plug" is installer shorthand for the same part — a coding resistor in a plug-style connector. Both terms refer to Vaillant part 0020266328 / 0020269259.
Is it a genuine Vaillant part?
The resistor sold through vheatc.site is a genuine OEM Vaillant component, new and in sealed Vaillant factory packaging with the part number printed on the bag.
Can I fit it myself?
We strongly recommend a Vaillant-approved installer fits the resistor and commissions cooling. It keeps the work within warranty terms and ensures the system is configured safely.