baxi combi 105e diverter valve?

hi i have a baxi combi 105e boiler and i have been having a problem with this when i have been turning the hot water on my radiators have been getting hot even though my heating is turned off. I have been told that this is my diverter valve i have also been told that i can get a repair kit for this could you tell me what this is and if at all possible give me a part number