Radiator (recessed convector) Bleeding Issues

CHomes

Hi folks,

Background:

1960 home with original hot water heating system with recessed convectors. Old style expansion tank up in rafters.

Convector #1 in system is on 2nd floor, would always get air locked and required a bleed every 3 weeks or so in winter.

Did all the usual checks for leaks etc. Turned off water supply and pressure held long term.

Eventually caved and had an auto bleeder put on only that radiator problematic. That radiator now has 0 issues.

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Now onto my question.

The next 2 convectors upstairs in the adjacent rooms, which never had issues before, now get air locked and need to be held basically every few days.

I was thinking that since my auto bleeder is on the #1 convector and it's up on the second floor that this auto bleeder would relieve the majority of the air in the system. (made sense this would be where most of the air went to find a home).

Could the auto bleeder be sucking air into the system thus causing the next few convectors to air lock so fast?

I realized one mistake I may have been making: should I be closing the auto bleeder in the #1 convector when I bleed the radiator in the next room? I have not been closing it. Could the act of bleeding the radiator in the next room be causing the auto bleeder in the first room to suck air in? I plan to try to bleed again today after closing the auto bleeder. However...if that was causing air to be sucked in, wouldn't it just suck in later once I re open it due to built up suction?

Thanks for any thoughts or help!

PS - I probably really need a new boiler or at least some repiping but not sure how much longer I want to stay in this house.