On 07/11/17 10:29, AnthonyL wrote:
I need to ensure I've got all the air out of my closed pressurised
system in order to resolve/eliminate another issue. Pressure is
around 0.8bar when I start, down to about 0.5bar when I've finished
and I then repressurise.

The bleed screws are those little square ones at the back (not side)
of each radiator so when they squirt out they hit the wallpaper.

The property is a bungalow so all radiators at ground level but the
pipes go up and over via the attic.

I'm debugging a similar (and new) system - my pipe runs are tortuous out
of necessity (upstairs is a dormer, so pipes go:

Up from boiler

Down to north side rads.

Down to interlink pipe to south side.

Up to distribution pipework

Down to rads.


Needless to say, the south side has two cold rads on the ends of the
distribution leg.

Trouble was expected - so after seeing how naive pipework behaves
(better than expected to be honest) I'm getting the plumbers back to
insert bottle type auto vents in several key locations once I can
determined where specifically the air seemed to be getting trapped.

A thermal camera would be dead useful here - are those hireable?

Otherwise, we'll do it the old fashioned way by feeling the pipes for
the lukewarm (neither hot flow nor cold return) bits.


So probably the same for you - add some bleeders in the high bits,
especially the returns.


Anyhow most of the radiators instantly let out a silent stream of
water.

They would generally - the air locks are in the pipe above.


A couple sputter, water comes out but with a sputtering sound and/or a
whistling sound and this is where I'm confused. It seems no matter
how much I let out (I'm talking cup fulls not gallons) they still seem
to sputter. They sputtered yesterday, today and I expect they will
tomorrow.

Is this air in the system or is it just the shape of the screw?

Probably air - you'll find there are one or two rads that seem to catch
odd bubbles of air that the pump manages to shove down a pipe.

Am I correct in assuming that air cannot be introduced into the system
unless there is serious corrosion or the like going on?

Correct.


How much oxygen am I reintroducing repressurising the system?


It won't matter if you add inhibitor.