continuing air problem in central heating piping

[tellme_why]

Hello all,
My central heating is open type fully pumped; air keep developing in the piping despite I bleed radiators almost daily. What's the issue?
At one time I suspected the radiators pipes leak in the suspended floor, but could not prove it yet.
Looking at https://www.pearsonschoolsandfecoll...FreesamplechapterPlumbing/Level2_PLUMB_SB.pdf
I noted two issues with my piping: 1) there is no air separator illustrated on page 316 of the link
2) The water level in the F&E cistern is not below the water level of the CWSC (see page 316 of the link)..
The problem exacerbated recently when a plumber installed bulldog TRVs as well as connected new design radiators that "use a lot of water" in lieu of old panel radiators..

The air is burping all day, noisy and you can hear it running from ground floor to top floor all the time...
Any idea how to fix this??

many thanks

 

[Lower]

I would check to see if there is pumping over going on. If the new TRV's are creating too much of a restriction you might find that every time the pump starts up a dollop of water is pushed out of the vent pipe into the tank. That will entrain air into the water that in turn will end up in the radiators.