got called out today to a jaguar boiler about 8 years old. complaint of no hot water but heating ok.not familiar with jag boilers. cant hear the diverter valve changing over so im assuming its gone. is this a common fault with this boiler? or is it more likely to be a sludged dhw heat exchanger?anyone familiar with this boiler? also how easy is it to change the diverter valve is it a strip down job? any help would be appreciated