Longevity is largely a function of how much water has moved through the tank. In an intermittently used vacation house an 18 year old water heater may have only seen three to five "normal" years of water flow through the tank, and could easily go for another decade.
When the place won't be occupied for several days or weeks, turn off the water & power to the tank.
Dana,
Thanks for the reply. From what I understand the first 16 years the owner rarely stayed at the house. Only the last 18 months was it occupied 100% of the time.
We always turn off water and water heater power whenever we leave any house, even when gone just for one night.
I think I’ll pull the anode on the tank and if it doesn’t look REAL BAD I’ll install a powered anode and a Honeywell AMX300TLF mixing valve. I like the AMX300TLF valve because it allows me to turn up the tank heat to 140 deg and still feed 120 deg water to the fixtures. The 140 deg I feel helps kill bacteria. I could easily return the water heater to HD.
I think I’ll patch the plastic water heater pan with some eternabond tape that I keep for my RV.
If I run into trouble I can always throw in the new tank.