In message ,
Timothy Smith writes
I drained our combi system three or four months back and when I refilled
it I forgot to add inhibitor.

Now Ive remembered Im trying to figure out where to add it. The only
possibles are the filling valve or a radiator bleed valve as far as I can
see.

Can anyone tell me the correct method ?

Any that works?

You can get Fernox inhibitor in a big syringe type affair that attaches
to the top tappings on the radiator.

I put it normally via one of the upstairs radiators. We used to have a
ladder type radiator in the bathroom, this was easiest. Drain down the
system a little, remove one of the plugs from the top tappings, stick in
a funnel pour in inhibitor. Replace plug, top up system and
repressurise.

When we didn't have a ladder radiator I had a a bit of flexible plastic
pipe - in this case 15mm Hep2O pipe - but hose pipe or whatever is
around, a compression - to - threaded fitting on the end. Screwed this
into the top tapping on the radiator and put the funnel in that.
--
Chris French