house was re rendered last year. one area was badly spalled around are below a rwp which passed into wall. Old render was removed. Now notice same is happening to new render. Any advice?

has the source of the problem been rectified leaking rwp ?

It would help to know if the rwp is in old cast iron or plastic, what it specifically picks up and it's known route down through the building structure / details of where it passes through the wall and proximaty of any other elements of the structure that could be suspect. Is the internal face of the wall accessible where the pipe passes through and is that showing any visible signs of damp? Generally though - very likely to be the pipe and/or any associated flashings at fault which are allowing water to penetrate the wall and in turn cause the render to spall.