I have an old house, built in late '20 -and lately problem with a
pressure in (hot water) heating system. Everything's been normal for
last couple of years but ... things change, I guess.

Problem: very soon after furnace gets signal from main thermostat in
the house, water starts to heat up. Water pump turns on (around 130F)
and the pressure builds up. So far everything seems normal but usually
after several hours pressure gets too high and security valve opens
and attempts to lower that pressure. You can imagine my surprise when
I first time saw that system is "leaking" and that a good part of my
basement is wet because of that.

To (temp) fix it I do the following:
-turn system off
-close valve that leads to the expansion tank
-remove water from the tank
-open the valve that connects expansion tank to the rest of the system
(that drops pressure to "normal value which is shown as 10-15 feet)
-turn system on

Settings on the thermostat is: 130F (when water pump kicks in) and
160F when heating stops

What could be wrong? How to setup termostat so system'd work as it
used to?
Thanks for the input.