If the SpeedComforts don’t start while the radiator is hot, it could be due to the supply temperature of your heating system. The SpeedComfort activates when the sensor detects a radiator temperature of 33 degrees. Check if your supply temperature is high enough. If it’s too low, for instance, with low-temperature heating, this could be why the fans aren’t running. For low-temperature heating, we have a low-temperature sensor that activates the SpeedComforts at 28 degrees. You can order this sensor in our SHOP.