Thanks juliusceasor, I will look into getting some local engineers to have a look at the system to make sure that there isn't a more serious underlying problem which needs to be corrected. In response to slick132, the boiler is made by Biasi (i'm sure on exact details as working away at the moment) - on the BG forms they always write Riva compact if that's any help. I think the pipes leading to radiators are 1/2 inch, I don't think they are as small as 6mm or 8mm anyway.

I came across this thread whilst doing a general search and wondered if someone can give me a little advice. I have two radiators that needed frequent bleeding and so I called BG out under my Homecare agreement. The engineer who came advised me that I need a powerflush as the water is dirty and so there is hydrogen building up in those two radiators. In the short term, I am quite happy to bleed the radiators every now and then whilst I save up to have the powerflush done. Long term though, the thought has occurred to me, that as my central heating system is quite old (its an ex-council house so not sure when the radiators etc were installed) would I be better saving for a bit longer and having all my radiators changed rather than a powerflush? Would this be a viable solution? Or will the system need powerflushing even if we changed all the radiators? Also, if I was to get a local firm to do the work rather than BG, does anyone know if this would invalidate my BG Homecare agreement?