I dont know why you changed anything, your problem is probably your
autofeed valve. You dont need to leave it on unless you have steam heat,
HW is a closed system. Drop your water pressure to 10-12 and see what
happens, keep the autofeed closed, if pressure increases more than 4lb
your expansion tank was and is to small. You only need enough pressure
to get water to the highest floor, I run mine at 12 and the boiler is in
the basement of 3 upper floors, a total of 4 floors. If the top floor
radiators get cold add a few more lb. Autofeeds are known to go bad,
turn it off, if level drops you have a leak to fix. Boilers last longest
at lowest pressures.