Heat radiators not all working
Judging from your pressure gauge your system pressure is far to low. You want the system to operate between 15 and 20psi. You need to make sure the pressure reducing valve is operating correctly and adding water/pressure to the system. Also make sure there is no valve closed going to the boiler fill line and pressure reducing valve. Some systems will just have a regular valve and it is up to you to add the right pressure to the system and then close the fill valve once complete.

You will also have to bleed any air from the system. You will need to have the system fill as you bleed it or else you will just remove more and more pressure instead of purging air.

If you can purge all the air and have the system fill back to 15psi your issues should go away. You will have to bleed out every radiator in the system to properly purge it.