What Model / Year of Peugeot do you have?
VIN number "vehicle identification number"?
How do you mean boils over? pushes out the cap or just froth/air bubbles?
Whats been checked/replaced so far upto now?
Thats not the VIN number...so can only go by all 407's with 2.0hdi's - As far as foaming goes/issues related there was a modified section of pipe as per High pressure hose Part number 4014.FP - RHD depends on the chassis number - But it doesnt mean to say the pump itself is at fault..normally these are eletrohydraulic as part of the reservior and are fairly common for causing that too..unless it the old mechanical assisted type with the pulley run pump you need to check the unions are leaking to the pump... As a starting point id say flush the system out and use the correct specified fluid,electrohydraulic pump FLUID DA 9730A5.but these are well known for requiring the level to be slightly overfilled to reduce foaming help during bleeding and see if that helps if you havent done so already....