How to properly refill the heating system with water

If the pressure is below the specified value, it is necessary to fill the system with water, or with a glycol mixture if the heating system is filled with it for protection against freezing. It is best to have a heating installer do it if you have no experience with floor heating systems, and since the procedure is simple and for systems filled with water, the equipment only requires a garden hose - you can learn it once you see how it is done and later do it yourself.
When the system is properly refilled, there is usually no need for venting, but it is still recommended that venting be done every time the system is refilled. The procedure is simple, and the tool requires a key for the vent valve on the radiators. After filling, turn on the pump and let it run for 2÷3 minutes. Then turn off the pump, wait 5÷6 minutes and carefully unscrew the vent valve on the radiator using a wrench. If there is air in the radiator, it will come out through the drain valve, and as soon as water starts leaking, close the valve quickly. Repeat the procedure on all radiators, and usually the most air is in the pipe dryer installed in the bathroom. Check the pressure after venting and add water again if necessary.