AK wrote:
I have been trying to bleed my radiators tonight and the top floor (a
3 story house) is just about as full of air as it could be. I have
bled loads out but after running downstairs 3 or 4 times to top up
the pressure in the system I have given up for the night. It occurs
to me that I am probably getting this because I don't have enough (if
any) treatment in the system. the house is 18 months old and I would
bet the developer didn't put anything in....................the water
is nice and clear what is coming out.

I would like some advice as to what I need to put in - I have to
replace one of the bleed valves (if that's not what they are called I
would appreciate knowing what it is called so I don't look silly when
asking for one!) as it doesn't tighten properly and I understand you
can put it in to the system that way - perfect as I have so much air
space in there!!

The bleed valves are the ones at the tops of the radiators which you
open to let air out. I've never seen one fail though. They're not all
the same size: some have just the little pointed-ended screw going into
a threaded hole in the steel of the rad itself, on others the ponty
screw goes into a brass (or chromed) bush which screws into a bigger
hole in the rad. Usually these bushes are the same size as the screw
threads of the rad valves, and there's a blanking plug at the other end
of the top of the rad (so the rad has four same-sized threaded holes, at
each end, top and bottom). Best to take the radiator along to the
plumbers' merchants ;-)

The stuff you get to squirt in through the bleed hole costs an arm and a
leg: better to get ordinary liquid inhibitor. If you have a partly empty
radiator (you can turn off both valves and loosen one valve-to-rad
connecting nut to let out water) and the sort of bleed valve in a bush
that's the same size as the valve threads then you can unscrew the bush
and pour in your inhibitor using a tube and funnel or squeezy liquid
bottle etc. Otherwise a pump-up garden sprayer adapted to fit the
filling hose for the system can be used to squirt in liquid inhibitor
(assuming you have a filling hose rather than special filling key).

Use Fernox MB1 or Sentinel X100 not Purimachos Protex.