fourth year
The relief valves on the other tanks may have been corroded so they could not work, especially if they were more than a couple of years old. The relief valve on a properly installed water heater must either go to an approved drain or to the outside of the building within 9″ of the ground. This requirement is to prevent the exact situation you have, and also to prevent a flood in the house if it should do its main job and open completely to prevent a dangerous situation.
