It very much depends on the installation as to whether the Alde system is as good as it is proclaimed to be.
We have had two caravans, both with Alde and they were very different. One, you set the temperature to 19 or so and it was brilliant. The second one, a Bailey, was rubbish. It heated up to inferno levels at one end and was cold at the other.
We have just gone to a new van with blown air, and personally I prefer it, as its heat is uniform across all the outlets, including the bathroom.
If yours is not functioning like it should do, check the air vents to make sure there is no air in the system. It should not push liquid out of the header tank, if it does, the cap is not on properly. It definitely swirls around in there (I'm assuming your van has the motor in the header tank) but shouldn't come out. Make sure the cap is clicked on.
Also, as I say, check the breather points (there will be several at the high points in the system) to make sure no air is trapped.