Definition
What is a Vaillant cooling resistor?
The small blue plug that unlocks cooling on aroTHERM Plus heat pumps
The Vaillant cooling resistor is a small coding plug — often called a "code plug" or "cooling plug" — that tells a Vaillant aroTHERM Plus heat pump it is permitted to run in cooling mode. On a heat pump supplied without cooling, the cooling option stays unavailable until it is fitted. This page explains what it is, why a heat pump needs one, its two part numbers, and what it does not do.
Updated
Buy the Vaillant cooling plug on eBay
Same blue plug, two packs. Choose the boxed 0020269259, or get the identical 0020266328 for a fraction of the price.
Original Vaillant box, labelled “Coding plug, cooling function”
Buy on eBaySold by eBay seller boarder895 · 100% positive feedback · 600+ feedback · on eBay since 2003 · 20+ plugs sold
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’s control electronics read the plug and, once it is present, make cooling available for an installer to set up.
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. The two have been compared side by side — same plug, interchangeable.
Why a heat pump needs a plug to cool
A Vaillant aroTHERM Plus 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.
Many of these heat pumps are supplied set up for heating and hot water only, with cooling treated as a deliberately enabled option. The coding plug 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 blue plug on a white two-pin connector, with a resistor inside — which is why installers call it a code plug or cooling resistor. It fits a defined coding position in the heat pump wiring, and the controller reads its value as the signal that cooling is permitted.
What the plug does — and what it does not do
The plug does
Authorise the heat pump firmware to permit cooling mode — the firmware state known as Authorised Cooling Mode. On a unit supplied without cooling, the option stays unavailable until it is fitted.
The plug 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", "cooling plug", "cooling resistor", "cooling chip", "cooling dongle" and "coding key" are all names owners and installers use for the same part — a coding resistor in a plug-style connector. Vaillant sells it as 0020269259 ("Coding plug, cooling function"), and the same plug also comes as 0020266328.
Is the one sold on eBay a genuine Vaillant part?
Yes. Both versions sold by eBay seller boarder895 are genuine Vaillant parts, new and unused — 0020269259 in its Vaillant box, and 0020266328 in a Vaillant small-parts bag with the part number on the label.
Can I fit it myself?
Have a Vaillant-approved installer fit the plug and commission cooling. It means working inside the heat pump, the installer can confirm the work sits within your guarantee terms, and the installer also has to enable cooling in the installer menu.
Related guides
Ready to buy? Both plugs are on eBay
The plug inside is the same — choose the pack. 0020266328 is the best value; 0020269259 comes boxed and labelled “Coding plug, cooling function”.
Original Vaillant box, labelled “Coding plug, cooling function”
Buy on eBaySold by eBay seller boarder895 · 100% positive feedback · 600+ feedback · on eBay since 2003 · 20+ plugs sold
provenance: sha256:4292cb37c3238c4b… · machine-readable: claims.json · llms.txt