Alde Fluid Loss

Ours is a 590 which has a transverse double bed as opposed to a french bed But I think the layout is otherwise similar  I have only. Found 3 bleed points one in the washroom, one to the right of the door as you enter the van and one in the wardrobe next to the fridge.  It seems strange it is dropping fulfilling even when it is not pressurised.  I assume your header tank has only one inlet plus a breather pipe so it acts as an expansion tank and the fluid doesn’t circulate through it?  I found Alde to be very helpful, but I did send them some pictures because our’s at least is not standard issue. 

One thing I should have mentioned is that the fluid loss rate is the same even when the caravan is not in use.

Noe that dd surprise me.

Apologies for a delay in replying, I'm currently in the caravan on Anglesey with just 3g signal so have limited internet. Further to Boff's post my expansion tank has the following. One large black rubber hose connected to the base of the expansion tank (the same type as those joining up the various foil radiators). A further small diameter plastic tube which enters the expansion tank near the top left side. It has no fluid but has some condensation and a few bubbles. I presume this is the breather pipe. Finally there is a screw top cap with a short vent pipe to allow any topping up and any over fill to escape. I have the three bleed points in the same position as yours Boff.. Regards Tirril