Got a worcester 24i couple of years old got an intermittent fault with heating and hot water. You can turn on manually in the morning and it may may not fire up and sometimes it does then goes off after 5 mins. funnily enough if you rattle the bottom panel where the dials are youll heare a humming noise then boiler fires absolutely crazy any ideas?pressure fine and when its working ok which it can for hours on end water really hot and radiators piping crazy