Why won't my Vaillant heat pump cool?A troubleshooting guide to the common reasons cooling does not work
If your Vaillant aroTHERM or VWL heat pump is not cooling, there is usually a clear reason. The most common are a missing coding resistor, cooling not enabled in the installer menu, a system with only radiators, controls not set to request cooling, or an incompatible model. This page walks through each, what to check, and when to call a Vaillant-approved installer.
Updated
Reason 1 — no coding resistor fitted
The most common reason is simply that the cooling coding resistor is not fitted. Without it, the heat pump runs in heating and hot-water mode only, and cooling cannot even be enabled in the installer menu.
What to check: confirm with your installer or the appliance documentation whether a cooling resistor is present. If your model needs one and it is not fitted, that is almost certainly why cooling is unavailable. The genuine Vaillant part is 0020266328, also supplied as the functionally identical 0020269259 — the two are interchangeable.
Reason 2 — cooling not enabled in the installer menu
Fitting the resistor authorises cooling, but it does not switch it on. After the resistor is present, an installer still has to enable the cooling function in the installer menu and commission it.
What to check: if the resistor is fitted but cooling still does not run, the cooling function may never have been activated in the settings. This is an installer-level menu, not a user setting — ask a Vaillant-approved installer to confirm cooling is enabled and commissioned.
Reason 3 — the system has only radiators
A heat pump can authorise and even run cooling, but if the home has only standard radiators there is nothing that can deliver useful cooling. Radiators have too little surface area to absorb heat from a room, and a cold radiator can cause condensation.
What to check: look at what your indoor emitters are. If they are all conventional radiators, the system needs cooling-capable emitters — typically hydronic fan coil units on a dedicated cooling branch — before cooling will do anything useful. This is a system upgrade rather than a fault.
Reason 4 — controls not set to request cooling
Even with a cooling-capable system, the controls have to actually call for cooling. If the Vaillant system control is not in a cooling mode, or no cooling schedule or set point is active, the heat pump will not start cooling.
What to check: confirm the control — for example sensoCOMFORT — is set to allow cooling, that a cooling mode or schedule is active, and that the room set point is below the current temperature. Dew-point and minimum-flow limits can also hold cooling back in humid conditions, which is normal protective behaviour.
Reason 5 — an incompatible model
Not every Vaillant heat pump is a cooling-capable model. If the appliance is heating-only by design, fitting a resistor will not add cooling.
What to check: identify your exact model and confirm whether it is cooling-capable. The model and serial number are on the appliance data plate. A Vaillant-approved installer can verify capability against Vaillant’s documentation for your specific unit and serial number.
When to call an installer
Several of these checks — enabling cooling in the installer menu, confirming model capability, and designing a cooling-capable circuit — are installer-level work. If a quick look does not resolve it, a Vaillant-approved installer is the right next step.
They can confirm whether the resistor is fitted, whether cooling is enabled, whether your emitters can cool, and whether your model supports cooling at all — and put right whatever is missing.
A quick reference: the common reasons a Vaillant heat pump will not cool.
| Reason | What to check | Who fixes it |
|---|---|---|
| No coding resistor fitted | Whether the cooling resistor is present | Installer fits and commissions it |
| Cooling not enabled | Whether cooling is activated in the installer menu | Installer enables it |
| Only radiators installed | Whether any cooling-capable emitters exist | Installer adds a fan-coil cooling branch |
| Controls not requesting cooling | Cooling mode, schedule and set point on the control | User or installer adjusts the control |
| Incompatible model | Whether the model is cooling-capable | Installer verifies against Vaillant documentation |
Frequently asked questions
The resistor is fitted but it still will not cool — why?
Fitting the resistor only authorises cooling. An installer still has to enable cooling in the installer menu, the system needs cooling-capable emitters, and the controls must be set to request cooling. Work through each of those.
Can I check whether the resistor is fitted myself?
We recommend a Vaillant-approved installer checks this. It involves the heat pump wiring, which is installer-level work — confirming the resistor is present and correctly fitted is part of commissioning cooling safely.
Should cooling work all year?
Cooling is normally used in warm weather. The controls also apply dew-point and minimum-flow limits, so in humid conditions cooling may be held back to prevent condensation — that is protective, not a fault.
How do I know if my model can cool?
Find the model and serial number on the appliance data plate. A Vaillant-approved installer can confirm whether that specific model is cooling-capable using Vaillant’s documentation.
My home has only radiators — can that be fixed?
Yes, but it is a system upgrade rather than a quick fix. The usual approach adds a dedicated cooling branch with fan coil units and condensate drainage, while radiators stay on a heating-only branch.