Replacing M3 174a 30PSI PRV

Hi. The Pressure relief valve on my hydronic water heating furnace is leaking.
It's a 3/4 *3/4 inch female both inlet and outlet. I can see that the exact model is available but is there any interchange?
Also I see that someone stubbed out a pipe on the outlet side (which is closed off) inside the furnace room. The outlet to the outside is of course open. I am wondering why it would be stubbed out.
Photo shows detail.
Thanks
Ian

seems the photo did not attach

I bet you a donut..someone did not have a coupling with them....so they used a tee and cap.

before you replace,

hold your channel locks firmly in your hand, knock the hell out of that valve. give it a good wrap up side the valve.

check and see if its still dripping...sometimes that makes it seat...

if not



just take that one out and replace.

shut down boiler
close all valves
kill gas or turn off breaker

remove an replace.

drink beer

the new valve. never!!!!!! open the valve. leave it the hell alone.
when its opened, trash, gets on the rubber diaphragm, makes it dribble like a old mans prostate

Hey Frodo, Thanks for the advice. I tried the valve beating, but still dripping. Any suggestions of a good online source for this valve or an equivalent?
Thanks
Ian

ho depot ? google the valve number,