Hot Water Failing?

My Midas SI has problems sustaining hot domestic water, the heating system is ok, the hot water works for a time then fails, when fails the temp will not move from 30c however when the temp does move to 60c the hot water works, I have been told by an engineer to buy a new boiler, there must be just a part failing to sustain the temp needed for constant hot water

Geoff Husband
February 2011