If opening the thermosiphon purge valve the air comes out initially and not water means that there was still air.
The cause of this lies in the boiler or in the emptying of the system during work.
This is not a problem, just purge all the heaters with a little patience. If this operation is not carried out, in fact the yield will drop considerably.
In fact, you will notice the presence of air even if you touch the radiator, in fact the upper part will be colder because; occupied by the air bubble and not by the hot water coming from the boiler.
How to eliminate air
Switch off the boiler. At this point, very patiently, vent the air through the appropriate valve until a steady stream of water comes out of each radiator at home.
- Check the system pressure at the beginning of the operation.
- At the end of the air purge, reset the original operating pressure of the system with the appropriate tap on the boiler
- Now you can turn the boiler back on, your radiators will return to their maximum efficiency