Draining gravity back boiler

[heheshamon]

Hi I could do with a bit of guidance to empty my system to clean and inhibit it I think I'm on the right track with the below method but would like someone who does this as a profession to double check, I have had to put up with some knocking pipes this winter (1st time since moving in 14 years), I emptied the system a few months back but there must be some dirt left as it came back in a few weeks.

my question mainly which I'm quite confused with is I have three radiators down stairs but they all have drop feed and return pipes and only two of the radiators have drains, is this normal as this won't drain the complete system?

Would it be best to drain the system as much as I can then shut the valves on the last one and remove the radiator (as if it was being replaced) drain the remainder of the water from the two pipes (what type of fitting would I need for this?) and then add a drain onto this radiator as well.

after I have done this there would still be water going down to the pump side would the cleaner/ inhibitor do its job with this water i.e. Would it push the dirt round the system and would it be ok to leave that much diluted cleaner in the system when I drain to put the inhibitor in.

thanks very much in advance.

 

[Alex Knight]

Just fill and drain 2 or 3 times circulating the water between each drain down

 

[PlumbBobBob]

you could use a self tapping drain off then fit permanent drain off after like this
http://cdn.toolstation.com/images/141020-UK/800/50376.jpg