Hi Ofer,

Do you know where the leakage was from, other than "the inside part of the water heater"?  Having had 5 tanks fail in the 5 years since you got the boat is pretty amazing. Have you asked the factory or your mechanic what the problem has been?  Was it the same for all 5 heaters?

If you have an interest in chasing this down yourself you can take off the decorative SS jacket of a failed unit, then remove the insulation jacket, fill the tank and turn it on and perhaps see exactly where the "inside part" is leaking. You'll want it to get hot since it may only leak when it's hot.  As Yogi Berra said, "You can observe a lot by looking around".

I did see a post on another db that Isotemp had to redesign the thermostat circuitry of the Basic model because the heating coil wasn't being shut off and that caused overheating that distorted the tank, but that doesn't sound like your issue.

Years ago I had leakage from the bottom of my tank from pin holes of corrosion from particles of heating elements that had broken off when I replaced them. I cleaned them out and patched with JB Weld years ago. Certainly not your problem with brand new units repeatedly failing (mine is now 15 years old).

Good luck with it,
Craig
Craig