The old plastic model has been replaced by a plate heat exchanger and a re-pipe kit.
Check with some where like plumbcentre for part no. but don't by it from them . Small independent suppliers are usually cheaper(depending where you are).
Word of warning: There are copy kits available and some are pretty cheap and nasty. Also the instructions in the genuine kits require that as well as fitting the heat exchanger you also have to fit a new valve seat in the diverter valve and possibly alter the links on the P.C.B..
T.h.s
July 2007