Boiler makes noise?

Hi there,
My Potterton Suprima 50 boiler is making a clanging noise. I bled the system, however, the problem persists. I tried to listen to the noise of the boiler and realised that the water in the system overheats to the boiling point and that is the reason (I hope I am right). I assume that the pump that circulates the water in the system is broken. Am I right?
Thank you.

Igor
January 2009