Bleeding heating / radiators, how far do you have to unscrew the radiator?

Hello! Sorry for opening two threads in a row.

But I have a question about bleeding radiators. I know that you unscrew something on radiators so that some water comes out. But how much should that be approximately? Just a little, or a cup, or, or, or..?

And one more thing: The radiator in our place is really humming. Is that normal, or is it related to bleeding?

Thanks

You have to bleed the radiator (i.e., open the screw at the top/end face of the radiator) until no air and only water comes out. Once this flows out, you can close it again. Warning: Always keep the small key ready in your fingers or keep them "on it," because after a short "gurgling," the water will come out. Hold the cup or glass at an angle so that the water (under pressure) does not splash onto the room or against the wall.

The humming of the radiator has nothing to do with air. Here you would hear more of a bubbling or gurgling sound. If it bothers or worries you, have it checked by a professional.

As long as air is still coming out, you have to continue bleeding. Only when all the air is out is it good. But it is not enough to do it just once, I would do it again after a few days because the air often only fully leaves the pipes after a few days. As long as it gurgles, you are not finished with it yet.

You have to turn the screw until the air has escaped.