Definition
Active vs passive cooling on heat pumps
Compressor cooling vs natural cooling — how they differ
Heat pumps can cool a home in two ways: active cooling, which runs the compressor, and passive cooling, which does not. They suit different systems and deliver different results. This page compares them and explains which Vaillant systems use each.
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
Active cooling
Active cooling runs the heat pump compressor in reverse to actively chill the water sent to your indoor units. It delivers stronger, more controllable cooling and works on air-source systems such as the aroTHERM Plus. It uses more electricity than passive cooling because the compressor is running.
Passive cooling
Passive cooling moves heat from the home into a cool heat sink — typically the ground, via a ground-source heat pump’s buried collector or borehole — without running the compressor for cooling. It is very cheap to run, but the cooling effect is gentler and depends on having a suitable ground loop.
Vaillant’s documentation describes a passive cooling module for its flexoTHERM and flexoCOMPACT ground-source systems. Check the documentation for your own unit.
A side-by-side summary. The right choice depends on your heat pump type and what is already installed.
| Aspect | Active cooling | Passive cooling |
|---|---|---|
| Compressor | Runs for cooling | Not used for cooling |
| Typical heat pump | Air-source (aroTHERM Plus) and others | Ground-source (flexoTHERM) |
| Cooling strength | Stronger, more controllable | Gentler |
| Running cost | Low — but higher than passive | Very low |
| Main requirement | Cooling plug (where needed) + installer activation | Suitable ground loop |
Frequently asked questions
Which is better?
Neither is universally better. Active cooling gives stronger cooling and suits air-source heat pumps; passive cooling is cheaper to run but needs a ground loop and gives gentler cooling.
Which does an aroTHERM Plus use?
The aroTHERM Plus is air-source and uses active cooling. On units supplied without cooling, enabling it needs the cooling plug fitted and cooling activated by an installer.
Do both need a coding plug?
The cooling plug sold on eBay (0020266328 / 0020269259) is listed for aroTHERM Plus air-source heat pumps. Ground-source cooling is set up differently — check your model’s documentation or ask a Vaillant-approved installer.
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
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