Draining & refilling central heating system


I am considering cleaning out my 8,5 year old heating system and refilling with corrosion inhibitor.
I've had a good look around the plumming and it appears to be a closed one, fired by a Potterton Suprima gas boiler. It is so closed that I'm unable to locate any drain or filling valves.
I also feel the circuit pressure may be low at 1bar.
So, I would greatly appreciate if anyone had advice on draining & filling of the system and the advised pumping pressure.
Many thanks, Brian
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snipped-for-privacy@yahoo.fr wrote:

Try looking near your ground floor radiators, there should be a valve to allow the system to be emtied, a small stubby pipe with a square head. If not the plumber was a cowboy!
If there isn't one, removing a valve from a radiator would allow the water to escape but I've no idea how you'd attache a pipe to drain it cleanly into a darain.
There should be some way of draining the boiler but this will only drain the system down to the boilers level so could leave it half full.
Mike
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wrote:

In such a case close both valves to the radiator and remove the rad (catching the water in a litter tray or some such container). The connection of a hosepipe to the valve will then be 1/2 inch or 3/4 inch BSP or 15 mm compression depending on make of valve.
Adam
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