how can i fix my worcester 24cdi boiler?

the digistat which is less than twelve months old has stopped working and recently the shower which runs through the combi boiler runs cold, the boiler is not kicking in even if i turn off the central heating the bath and sink tap occasionally runs hot upstairs but the boiler kicks in when i use the tap in the kitchen which runs hot all the time . could anyone please advise me of what the problem might be, i do not have an instruction book.