Air in the central heating system is bad for the system. The central heating boiler has to work harder to heat your house, which costs extra energy.
Taps and other noises: venting
The central heating system should not make any noise in the radiators and pipes. If you hear the water flowing or if you hear tapping, you must vent the radiators. If the entire radiator does not warm up, you should also vent. If you do not know how to vent the system, check YouTube to see how to do it.
How do I vent the central heating?
Remove the plug from the central heating boiler. Wait at least 10 minutes before starting. You can skip this step if you have just refilled the boiler.
Take the bleed key and a cloth. Start with the radiator at the lowest point in your house. Then work upwards and finish with the radiator at the highest point.
Place the bleed key on the air vent located at the top of the radiator.
Turn it a little to the left. Hold the cloth in front of the spout of the air vent.
As soon as water comes out of the valve, you can close it.
Repeat this with all radiators.
Put the plug of the central heating boiler back into the wall socket.