Most property owners attempt to save as much as they can after a flood. Appliances with complex electronics generally must be replaced, but simpler ones such as gas water heaters might be salvageable. A certified plumber is always the best resource to repair (or replace) major flood damage, but the relighting process is fairly simple. Add a few more steps to the process to make sure that your water heater is safely re-lit.
Turn off the gas supply if you didn’t get a chance to turn it off before the flood. Turn the gas control valve to the off position. Allow the water heater to sit until it is completely dry.
Sweep as much dry muck off the water heater as possible, and clean all the supply lines, the overflow line and drain with a soft cloth. Use vinegar as a cleaning solvent.
Remove the front plates at the bottom of the tank, and clear the burner holes out with a toothbrush or other small, soft brush—again using vinegar as a solvent. Replace the thermocouple or any other parts that have been damaged.
Allow parts to dry completely again, and attach connections for the thermocouple, pilot and gas supply if you’ve detached them. Check each gas connection to make sure it is tight enough by dropping a bit of dish washing soap on it; avoid over-tightening gas line connections.
Turn the gas supply back on, turn the dial on the gas valve to the “pilot” position and depress the push-button pilot button as you light the pilot under the burner with the log lighter. Hold the pilot button down to “prime” the thermocouple—otherwise it will cut the gas supply to the pilot light.
Release the pilot button, and adjust the temperature dial to “vacation” or “pilot” position. Turn the gas valve to “on” position, then slowly turn the temperature dial clockwise until the burner “fires up.”
Turn the temperature valve down once you’re sure the burner fires properly. Replace the front panel on the tank, and reset the temperature valve to its customary position.