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All water heaters now days have limit switches on them. They heat up and the limit switch kicks it out of cycle and when you let it set for a minute it cools down and lets the unit start back up with the same problem, for safety reasons you need to replace the limit switch that is bad. However to check for a bad one disconnect the wires on each side and put a car fuse in its place to see if the cycle stays on. The limit switch is round with a spade connection on each side. You can also see it in the schematic on the inside of the cover.