The idea is to depressurise, not drain. The drain cock will depressurise but if there is an auto air vent somewhere then it will keep draining.
I usually just open a radiator bleed screw and stand there with a bowl while the water pi$$es out until the pressure is 0 on the gauge. Make sure the filling loop / valve is properly closed.
Had one last week that had a PRV that had been letting by for months. Kept going 'cos the filling loop valve was also letting by!
I usually just open a radiator bleed screw and stand there with a bowl while the water pi$$es out until the pressure is 0 on the gauge. Make sure the filling loop / valve is properly closed.
Had one last week that had a PRV that had been letting by for months. Kept going 'cos the filling loop valve was also letting by!