How a Vaillant cooling resistor is fittedAn owner’s overview of where the resistor goes and what happens next
If you have ordered a Vaillant cooling resistor, it helps to understand how it is fitted — even though the actual fitting is an installer task. In short, the resistor plugs into a defined coding-plug position in the heat pump wiring, and the controller then recognises that cooling is permitted. This guide is an owner’s overview, not an installation manual: the work itself should be done by a competent, Vaillant-approved installer.
Updated
What the resistor is
The cooling resistor is a small resistor inside a plug-style connector housing — which is why installers call it a code plug. Vaillant supplies it as part 0020266328, and under the interchangeable number 0020269259. The two are functionally identical.
It is a passive component. There is nothing to program and no battery or software — its job is simply to present a fixed resistance value to the heat pump controller.
Where it plugs in
The resistor fits a defined coding-plug position in the heat pump wiring. The controller has an input that expects a coding plug; when the resistor is fitted there, the controller measures the resistance value.
The exact location varies by model, which is one reason fitting is an installer task — the installer works to your model’s installer manual to find and access the correct position safely.
What happens when it is fitted
Once the resistor is in place, the controller reads its value and recognises that cooling is permitted on the appliance. This is what unlocks the cooling option so it can appear in the installer menu.
Fitting the resistor does not switch cooling on by itself. It authorises cooling — the controller now knows cooling is allowed — but the function still has to be enabled and commissioned.
Why this is an installer job — and what comes next
Fitting the resistor means working safely inside the heat pump. We strongly recommend a Vaillant-approved installer carries out the work: it keeps the job within warranty terms and ensures the appliance is left safe.
Crucially, fitting must be followed by enabling cooling in the installer menu, and then commissioning. The installer enables the cooling function, configures dew-point and minimum flow settings, and tests the system. Only after that final step does your heat pump actually cool.
Fitting the resistor — and what it still leaves to do
Fitting the resistor does
Place the coding plug in the heat pump wiring so the controller recognises cooling is permitted and the cooling option becomes available in the installer menu.
Fitting the resistor does not
Switch cooling on. An installer must still enable the cooling function in the menu and commission the system before the heat pump will cool.
Frequently asked questions
Can I fit the cooling resistor myself?
We strongly recommend a Vaillant-approved installer fits it. It means working inside the heat pump, and professional fitting keeps the work within warranty terms and leaves the appliance safe.
Where exactly does the resistor go?
It plugs into a defined coding-plug position in the heat pump wiring. The exact location varies by model, so the installer works to your model’s installer manual to find it.
Will cooling work as soon as the resistor is fitted?
No. Fitting the resistor authorises cooling. An installer must still enable the cooling function in the installer menu and commission the system before it will cool.
Does it matter whether I get 0020266328 or 0020269259?
No. Vaillant has supplied the cooling resistor under both numbers and they are functionally identical and interchangeable. Either part is fitted in the same way.
Can the resistor be removed again?
As a plug-style connector it is physically removable, but removing it withdraws the cooling authorisation. Any change to cooling configuration should be done by a Vaillant-approved installer.