Gurgling radiators

[Leard]

I've recently moved into a new home. There are two floors. The radiator on the top floor, and one of them on the first floor are gurgling when the central heating and radiator are on. I have bought a radiator bleed key to try and fix it. I've tried it on the first floor radiator and when I twist a little bit the radiator starts hissing out hot water. It doesn't just seem to be air being pumped out.

It's making me think that bleeding the radiators isn't the solution. Therefore what would be the solution?

 

[Stadan20]

Try bleeding them when your heating isn’t on . . When system is cold

 

[Leard]

I've tried that and it just dribbled water out rather than shoots it out.