Problems with Webasto / Thermocall TC4. Only cold air

Hey guys

I recently bought a 2016 Fabia with a Webasto auxiliary heater with GSM module. I received my SIM-card yesterday, and after a few tries and headaches, I finally got the thing working. However, the Webasto is not blowing any hot air into the car. The water is heating OK, but no hot air is coming in, until I turn on the ignition, and the climatronic is powered on. As soon as the ignition is on, plenty of hot air is pouring in. When the Webasto is turned on, the fan in the car is on almost full throttle, but it is only cold air coming in...  Does anyone have any suggestions for this problem? I have tried putting the climatronic to max heat before turning if off, but that does not help  :-(