Its probably the flow switch, shouldn't need a whole new diverter just a diaphram.
Neil (Baxi engineer)
August 2007
I don't know if it is the same thing, but my Vallient had the same fault recently and it needed a "diverter valve". It cost £350 for a plumber to fix it!
Ramases
August 2007
I can answer this question...
when select hot water i need to turn on heating as well?