no hot water evrything fires up?

Hi need help. Iv`e got a sime super90 I fitted a new diverter valve and micro switch about 8 months ago.
Everyhing was fine up to last week, for some reason the hot water stopped being hot, still get central heating but no hot water still runs cold. The boiler still fires up but still no hot water. If I leave the tap running the heat starts to come through the radiator
Is it possible the diverter needs replacing or hopfully something simple.(aye right) many thanks and all the best Gimmy20