whats wrong with my friendly format sime 80e combi bolier?

hi woke up today boiler not well any ideas what could be wrong? heating works fine,however problem with water you turn the tap on takes a few seconds for the water to start to get warm-it gets warm and remains like that,then you can hear the flame go out and the water goes cold again-flame will kick back in and reheat but it only seems to get to hand tempreture not boiling for a bath.have had probs over years since had it basically where the red light has come on and broke down completly but this is different any advice???water does nt seem to get hot?