Solid Brake Pedal problem on a Citroen Dispatch 1.9D Van (04 plate)?

Hi,

Can anyone help? We have recently purchased a Citroen Dispatch 1.9D van (04 Plate) not long after getting it home we noticed the brakes were not responding well. A week later the brake pedal went solid- very scary! We have replaced the front brake discs and pads, vacuum pump and pipe, non-return valve from pump to the servo. Still the problem persists, the brake pedal goes solid intermitantly. At present the van is totally unsafe to drive. Can anyone enlighten us on how we can rectify this fault.

Many thanks

Danielle & Andrew
June 2010