You should bleed radiators when they are cold, not hot. The recommended procedure is to first turn off your heating and allow the radiators to cool down before bleeding them. This is because bleeding a radiator when it is hot can cause hot water to spray out and risk injury. The proper way is to identify radiators that need bleeding (typically cold at the top or making noises) by running the heating on briefly, then turn it off to let them cool before starting the bleeding process. Open the bleed valve slowly with a radiator key until air escapes, and once water begins to flow steadily, close the valve. After bleeding, check the system pressure and repressurize if needed before turning the heating back on. This ensures safe and effective removal of trapped air, restoring efficient heat distribution without risk of burns or inefficient bleeding with the system actively circulating hot water.