how can i fix my kingfisher mf boiler?

system venting over boiler not shutting down on stat,overheat stat not cutting in either.new stat fitted and new overheat stat,boiler now appears to operate in heating mode but conrol box constantly clicks when stat kicks in,but boiler will still not shut down when in hot water only mode thinking of changing temp sensor but why is control box clicking,other than not switching off when at temp all other aspects of boiler appear to work fine