Best way to clean my system?

So.. I have a Boilermate 2000 with a Glow worm micron boiler, header tank in the loft.... Boiler seems to be functioning ok, no problem with controller board or sensors etc. but I get occsional pipe knocking when certain hot water taps are turned on (central heating does not cause this)... This may be related to me recently having to drain and refill my whole system after accidentally drilling through a pipe a few weeks ago.

My best guess is that by drainig and filling my system, a lot of junk from the radiators has been 'kicked up' and is now within my thermal store which is causing the knocking when I run certain taps... I assume due to thei being an open system it cannot be trapped air? So I have three questions:

1) Is there a 'staright forward' way to flush and clean my system to clean out some of the junk?

2) If the answer to the above is no, are additives worth a shot? What additives should I try and where can they be purchased for the cheapest price?

3) For future reference what is the correct procedure to drain... and then refill my system?

Any input appreciated.

Tim

Draining the unit / system
Will not be the cause of any knocking when drawing hot water.

Unless the DHW pump (far right on the unit is knocking.

Go through the post on BM 2000 's on here.
I have covered how to clean the system.

Mike
MGC/H2O
Norfolk