Unknown brand and type water heater.
Tank, hybrid, solar-assisted, indirect, tankless, condensing, gas, electric, under-counter, RV, mobile home, etc?
1) Water heater warranty-coverage does not require registration of product. Usually the registration can take place at manufacturer's site, but not all sites have registration forms.http://waterheatertimer.org/Water-heater-manufacturers.htmlhttp://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#warrantyhttp://waterheatertimer.org/How-to-maintain-water-heater.html
2) Almost all water heater warranties cover original owner, one-family household installation, when product is installed according to product manual. SO if you register product, then move to new home and take expensive water heater with you, then the registration does not show new address, thereby voiding product warranty because it was relocated.
3) Warranties after first year usually cover parts and tank. Many warranties today are pro-rated, which means longer warranty is becoming almost valueless.
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