how about MAYBE: you have a bad pressure gauge misleading you?
or MAYBE rust or dirt is bothering your pressure relief valve, with
insulated gloves open it up and flush it out its scalding water and
debris.
hunt down your nearest old time experienced plumber in your
neighborhood to call on.
your required pressure when hot to get to how many feet to the top
radiator needs to be marked with a permanent marker near your gauge by
you for your system. i need 25 pounds when running and heating to get
to the top of my third floor radiators from the basement boiler IN MY
SYSTEM for example.
you need to search google for the manual pdf for your boiler, read
about your system, discuss the repair and seasonal maintenance of your
particular accessories and how they interconnect with your friendly
local expert, and keep the manuals for the various devices dry in a big
2-1/2 gallon ziplock bag convenient to the devices.
you have an interesting system which makes heat and hot drinking water.