Problem with Ideal Isar HE24 Combi Boiler?

A few weeks ago my boiler stopped given hot water,but the central heating was constantly on even when we try turn it of it just wouldnt.a plumber come around and changed the pump which fixed the prblem however the central heating is still not turnng of, a plumber has come around but cant seem to figue the problem out. can any 1 help