myson unit 3 central heating pump?

my myson unit 3 central heating pump was causing the pipes to bang evrytime i started the heating up, when i checked the pump i noticed it had 2 speeds switch, so i flicked the switch to speed 1 and it stopped the banging, i would like to know why this is?any1 got any answers.....im guessing its due for replacing but want to know why it was causing the pipework to bang on speed setting 2?

emygee
January 2009

feel it with your hand when you start the system up and alter the speed you should feel a slight humming, faster on higher speeds. if not there is a nut in the middle of pump remove. that is the centre shaft see if thats going round. (but place a rag under pump if removing nut, it will drip water )

hi-spec plumbing
January 2007