Since you have a PVC check valve and it isn't busted, it wasn't frozen.
Brass won't break as quick as plastic, but your plastic isn't busted, so there's little sense in replacing it.
Replace the PRV, they rarely reseal after blowing the first time.
Click Here to learn how to correctly size or program a water softener.
CAUTION, as of Nov 12 2013 all YouTube videos showing how to rebuild a Clack valve have an error in them that can cause damage.