Communal boiler in a block of flats, hot water works well but radiators do not get warm enough

I will suggest you to not to have pump installed first let have the automatic air vent on your radiators so any air built up in your system goes by self or bled your radiator more often. Its all depends on what system they have in building speak to management team they will help you more then anyone els here. Because they know the what system is there.

Either way it always affects highest radiators in the system as these are more prone for air points to be at- especially where heating isn't used as much in the summer months. Sounds like a maintenance call to check in boiler or plant room system pressure topping up and bled at highest points. No need for more venting at high points - I'm sure system installation was commissioned and checked before handing over in the beginning..?? Just routine system check at this time. Hopefully this helps. Thanks pd

Yes , I agree with the gentleman.