1. Accept it is time to replace. The fact the PRV is blowing is because you have the temp jacked up. The fact it does not last long is you're substituting higher temp to increase run time. The hotter the water, the longer it will last (mixing) to get warm water. You have lost capacity in your tank.
2. Take specs on current tank and figure out if it will fit your needs over the next 10yrs. More kids? Any additions? Just size properly, both capacity and physical real estate.
3. If you can solder, you can handle this yourself. Research, very easy to do, but is dangerous if you wing it (fire, steam, pressure).
4. After installed, make sure expansion tank is properly sized. The more volume being heated, the more expansion.
5. Follow manufacturers recommendation and pressurize expansion tank bladder accordingly.
6. Crack a beer, watch for leaks and let her warm up
7. Take a hard look at all of your faucets and trims. Does it all say Moen on it? If not, when finished with beer drive to store or nearest showroom (take tracie of course) and check out all of our new offerings!
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