Well, unless you are able to inject it into the system using an adaptor for the magnetic filter, you've got to drain some water out somewhere. I would think it would take ages to get into the system via the header tank so perhaps isolate and drain a radiator or towel rail and add it into the empty rad?
How would you drain enough water from a radiator? If I close the valves and open the bleed will it allow me to take out enough fluid?
Easiest way if you have a heated towel rail is to turn off both valves, unscrew plug at top, siphon 2-3 litres out and replace with inhibitor.
And crack open a nut at one of the tails then yes, you just need a paint tray or similar to catch the water. The trick is getting it into the top of the rad. As suggested a towel rad is by far the easiest as you just pour it in the top, if you don't have one then a normal white rad is a bit more difficult unless you buy a rapid doser or make something up with a funnel and hose and then take your time.
Unless there is a towel warmer or filter where it can be added, I found the easiest way is to turn off the cold water supply to the expansion tank, drain off just enough water from the system so that only the expansion tank itself empties (rest of the system remains full). Then I take out a couple of pints or so extra (you'll have to judge how much your system needs) so that the pipe from the expansion tank to where it joins the heating system pipework is emptied, plus enough volume for the quantity of inhibitor being added. I empty the inhibitor into the expansion tank and watch it disappear, then restore the cold feed to the tank.
When I've done this, as the rest of the system remains full, It's avoided creating air locks and having to bleed all of the radiators afterwards.
I keep a bit of inhibitor back (quarter of a cup) to tip into the header tank as it's filling to treat the water that will be in there.
When I've done this, as the rest of the system remains full, It's avoided creating air locks and having to bleed all of the radiators afterwards.
I keep a bit of inhibitor back (quarter of a cup) to tip into the header tank as it's filling to treat the water that will be in there.
Be careful draining the F&E tank, if there is sludge in the bottom you will pull it into the system, best to manually empty the tank, give it a good clean before opening any drain points
Hopefully he will be OK, it's only just been refilled from recent work. The sludge will have gone into the system last time 