brake problem with peugot e7 2ltr hdi?

brakes at front only stick on when it is just standing with engine on, abs replaced,servo and master cylinder replaced though 2nd hand.all brake pipes and hoses replaced. we are beaty on this one at first we thought the front brakes were binding on after just 3 miles but now find just leaveing it standing with engine on for 15 mins they stick on. the servo was by passed to see if this would help but no just the same. 3 garages have had this van its a 04 peugot e7 as used by taxis. its doing our heads in trying to find what the problem is,can anyone HELP