Underfloor heating air-water heat pump. House too warm when the sun shines

So now I have read in the Rosa forum the explanation why it is wrong to operate a towel radiator. So nothing to do with extended heating surface.

As I understood it, the problem lies with the return flow.

If the towel radiator is connected to its own heating circuit, this is probably the shortest circuit and allows a high return temperature to flow back to the heat pump within the shortest time.
This then reduces the flow temperature, which is counterproductive.

Of course, you can throttle it, but never so little that it is advantageous.

Towelradiator

therefore the trend is increasingly towards purely electrically operated towel radiators

If the towel radiator is connected to its own heating circuit, this is probably the shortest circuit and within the shortest time allows a high return flow temperature to flow back to the heat pump. This then reduces the flow temperature, which is counterproductive.