Molten air and gases in service water turn into gas with the increase of water temperature and start to circulate with water in installation. Metal materials in the installation may cause noise,  circulation  impairments  and  cavitation in pumps just as corrosion Air penetration into radiators will lead to heat problems. As there is constant air intake into the system especially in installations without oxygen barrier where plastic pipe is used and underfloor heating installations, this problem is  bigger.