hi my hot water keeps cutting out?

hi i have a halstead ace high boiler that keeps cutting the hot water out one minute its there then it cuts out any ideas as i have changed the thermistors thinking it was them please help
stuart, May 2012
halstead ace high
47_333_??
No DHW at all?
diaphragm on DHW flow switch
Intermittant DHW?
plate heat exchanger

manwithnoname, May 2012
Try flow sensor

Sd, May 2012
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