Turn off the main water supply and shut off power or gas to the existing heater
Drain the old water heater completely
Remove the old water heater and clear the installation area
Check local codes, permits, and manufacturer requirements
Choose the correct tankless water heater size and fuel type
Confirm proper electrical capacity or gas line sizing
Mount the tankless unit securely on the wall
Install the required venting system for gas models
Install a condensate drain if required
Connect the cold water inlet and hot water outlet
Install shutoff valves, unions, and service valves
Connect the gas supply or electrical wiring
Install any required pressure relief valve and drain line
Flush the water lines before final connection
Turn on the water supply and check for leaks
Restore power or gas supply
Start the unit and verify proper operation
Test water temperature and adjust settings
Inspect venting, combustion, and exhaust for gas models
Schedule professional inspection if required by local code