Hello,

Have a forced hot water heating system. Typical 2 story Colonial house.

Have a valve that I have to replace in the main
household cold water line.

But, I don't want to mess up the heating system, as the pressure in it
is set correctly, etc. There is a valve on its water line, but I am very
reluctant to turn it closed, as it hasn't bee used for many years, and I
don't want to create a new problem.

Question: If I shut off the main Water Supply Line to the house, would
the pressure adj valve going to the furnace keep any backflow from the
upper story of the house flowing out when I remove the cold water valve ?

e.g., do these typical pressure valves have a check valve incorporated
into them ?

Thanks,
B.