Disappearing water

Hi Guys
Looking for some ideas. i am having a water problem with my TD5 My coolent tank is loosing water,???? I had the AA out yesterday as my car overheated on a journey. he topped up the expansion bottle. pressure tested the whole system ,gas checked it , he assured me there was no leaks in the system and the cylinder head was fine and water pumped checked i drove home 70 mile water level fine. drove 5 mile today, and no bloody water left in bottle tonight, i am stumped. please help

Many thanks
Andy

If as u say don't have any leaks, then there could have been an air pocket, when the air is expelied as it should via the header tank cap valve there is a void which the coolent fills leaving a low coolent level.

mine had me baffled for a week, then i saw it purely by chance out of the heater matrix pipe, it had been rubbing on the engine lift bracket, but what a job i had trying to find it!