When air becomes trapped in your central heating system, it can noticeably reduce the thermal output of your radiators. Air can get into the system when it is topped up with water, so you need to know how to bleed your central heating system.
It is advisable to wear gloves when bleeding the system, as the water may be hot.
Gently wrap an absorbent cloth around the bleed valve. Water may dribble from the valve when you turn it; the cloth will absorb the water and stop it from leaking all over the room.