Then Turtle Rouge should be aware that there's a very good chance he would be able to buy an overhaul kit for his PRV and fix it him/herself.
I know that I can buy overhaul kits for Watts pressure reducing valves. That kit comes with a new diaphragm, seat gasket, disk (which holds the seat gasket in place), screw (which holds the disk in place), strainer screen, strainer nut and strainer nut gasket. And, of course, there'll be printed literature that comes in the kit that explains how to go about replacing the parts. And that kit cost me about $25 every bit of 10 years ago.
If I were turtle rouge, I'd find the name of the manufacturer on the PRV, phone around to the plumbing wholesalers to find out who the local sales rep or agency for that manufacturer is, and find out from that rep or agent whether an overhaul kit is available. I expect most plumbing wholesalers will order it and sell it to him if he pays cash since they do for that oddball kind of stuff up here.
If it turns out the problem isn't just expansion in the water heater, it'd be worthwhile trying to fix the PRV him/herself before hiring someone to replace it.