hello for a few weeks ive had a noise coming from boiler,( only way i can describe it is a hum hum hum all the time when the heating is on, but can hear it louder upstairs tehn actually from boiler had it serviced a couple of weeks ago and bloke said it sounded like fan and said they can start to make a noise, but the past couple of days he boiler has been vibrating when u touch casing could this be the fan causing it? and if so does the noise and the vibration mean its on its way out replies much appreciated thnxs