In order to add an Inhibitor to my houses central heating system, I've attempted to drain the rads using a drain off c*ck near to the boiler on the ground floor, opening radiator vents on the first floor. That worked OK ( air being sucked into the vents ) so I tried the ground floor rads but they continued to have +ve pressure with water dribbling out of the vents.
This was still the case even though the water stopped flowing from the drain off c*ck - but the radiator vents are about a foot above it.
I'm probably making a beginers mistake but can't understand why these rads didn't also at least partially empty through the drain off c*ck.
I had stopped water refilling the header tank using it's input stop c*ck in the loft.
Eventually I gave up and finished the job without draining the ground floor radiators which I hope was OK given I was just trying to get the inhibitor into the system. But I would like to be able to drain the whole system for future maintenance jobs. Thanks in advance for suggestions.
Phil