Bleeding a radiator

Sponge

0.3 sounds awfully low. I have no idea what your system is, but every central heating system I've had has required a pressure of at least 1.0 bar. Usually recommended to keep it between 1.5-2 bar

uncle_buck_3

The system pressure should be somewhere between 1 bar (minimum) & 1.5 bar when the system is off & cold.

The pressure will rise when the system is on, but will return back down when the system is off & cold.