Turn off gas, water, and electrical power to the existing heater
Drain the old water heater completely
Disconnect the gas line, water lines, and venting
Remove the old unit safely
Place the new gas water heater in the correct location
Ensure required clearances and proper leveling
Install or connect the vent system according to local code and manufacturer instructions
Connect the cold-water inlet and hot-water outlet
Install a new approved gas shutoff valve if needed
Connect the gas supply line using approved materials and fittings
Check all gas connections for leaks with a soap solution
Install the temperature and pressure relief valve and discharge pipe
Fill the tank with water before turning on the gas
Purge air from the hot-water lines
Light the pilot or follow the manufacturer’s ignition procedure
Set the thermostat to the desired temperature
Verify proper burner operation and venting
Inspect all connections for leaks again
Restore power if the unit uses electrical components
Test hot water at fixtures
Follow local permits, codes, and inspection requirements