Hello. I need to drain my heating system down to do some work on it. I was wondering how you calculate how much water is in the system to add the correct quantity of inhibitor when refilling? Is it possible to add too much or just a waste of money?
Thanks.
Normal rule of thumb is 1 litre of x100/f1 (I preffer fernox but they might all be the same, you'll never know) per 10 single radiators, if there doubles then you should double it up.
You can add to much which then produces froth in the pump and stops circualtion so dont go crazy with it thinking more is always better, but its not an exact measurment so dont get to caught up on it, you need to go quite over board before too much is the problem.
as far as flushing goes, ideally, you drain down the whole system (including opening all the radiator bleed points to let air in and all current water out. while its empty give the F+E tank a clean out if it needs it so you dont fill it with the carp from there.
while its drained fit the filter, then add cleanser and fill+vent system, let it run for a week or so depending on the type you use (stay away from stronger products like x800 or anything that requires to be neutralised)
when ready, drain system fully as before, open filter and clean, refill system (dont add any inhibitor yet, vent and run system till you have circulation again.
Then repeat drain down. To do it right can be anything from 2 or 3 drain downs to a dozen depending on your system, youll know when your good as the water draining out could fill an empty bottle of coke or similar and be colourless (if its still got a strong tint of colour (brown) then theres still cleanser in there and you want it all out.
Once thats done, fill with water and inhibitors vent and run system, I usualy add another bottle of inhibitor in the F+E tank after (assuming you have one) so when bleeding rads in future or as system water is replaced in time it doesnt dilute as quick.