15 year old multi zone hotwater hydo baseboard and radiator

Every year I would turn on my heat I normally bleed all valves until only water comes out. Make sure no air is in the system. This has never been a problem until now. Now there seems to never be enough pressure in the system. I used to do this without the zone being open.

I know I have a check valve from the supply that regulates the water and pressure entering the system. Can this be the problem? The pressure gage on the boiler is low. around 5 psi at idle. Never looked when running. But even when running I am not able to bleed easily. When I open and get little release but can just be thermal expansion.

Does this mean my check valve is bad? I expect to always have a constant supply pressure in the system. What is the normal expected pressure on the check valve.