If my water heater was in a flood, do I need to replace it?
Yes. The Air-Conditioning, Heating and Refrigeration Institute (AHRI) recommends that any flood-damaged heating and cooling equipment be replaced, not repaired. From the AHRI website, as it pertains to water heaters:
"Whether your water heater is gas-fired, oil-fired or electric, if it was exposed to flood water, the unit should be replaced.
In a gas unit, valves and controls will likely corrode. In an electric unit, the thermostat and controls will likely corrode. In both types, the insulation surrounding the unit will be contaminated and will be nearly impossible to disinfect. Additionally, the insulation would take a long time to dry, leading to corrosion of the tank from the outside.
Even if water heater components have been cleaned and the unit seems to operate properly, parts may corrode in the future. Both gas and electric water heaters have a pressure relief valve that can corrode and stick after being exposed to flood water. Therefore, be sure to replace this valve as well."
(Taken from www.ahrinet.org)
At the suggestion of AHRI, be sure to have your inspection and replacement work performed by a qualified professional.