28i rsf is dual pass heat exchanger and does not have divertor assembly or diaphragm.
its definately just a worcester 28i??
if it is, there is not much to the dhw demand apart from flow switch then power to fan etc etc. my first thoughts would be flow switch so id rule that out first.
could be pcb fault, but sticking flow switch id start looking at first before changing pcb
(advice given based on 28i rsf) :-)
iain
September 2008