My question is how easy is it to flush the heating system?

if its a normal boiler (not combi) i did my own.SW off gas,sw off cold water supply to header tank (small top up tank in loft),open all bleed screws on all radiators,open drain valve (sticks out low down on an outside wall with a square head) use an adjustable spanner to open,it will take some time to drain the black gritty water out,then either close all & open cold supply & bleed air individually or (in my case) unbolt each radiator ,take into garden & flush with hose,refit & bleed.

David
October 2008