How to Maintain a Tankless Water Heater

Maintain your tankless water heater by flushing it annually with vinegar, cleaning the inlet filter monthly, and checking venting systems regularly to ensure optimal performance and longevity.

1. Kill the Power First. Switch off the electrical breaker for your tankless unit. For gas models, turn the gas valve to the off position. Allow the unit to cool completely before proceeding with any maintenance work.
2. Lock Down the Water. Locate the cold water inlet and hot water outlet isolation valves on your tankless heater. Turn both valves clockwise to close them completely. This prevents water from flowing through the unit during maintenance.
3. Purge the Filter Screen. Unscrew the cold water inlet connection and carefully remove the inlet filter screen. Rinse the filter under running water and scrub gently with an old toothbrush to remove mineral buildup and debris. Replace the filter if it appears damaged or severely clogged.
4. Install Your Vinegar Loop. Attach garden hoses to the hot and cold service valves using the manufacturer's flushing kit. Place the other end of the cold water hose into a bucket filled with 4 gallons of undiluted white vinegar. Position the hot water hose to drain into a separate bucket.
5. Dissolve the Mineral Scale. Open both service valves and use a small pump to circulate the vinegar through the heat exchanger for 45-90 minutes. The vinegar dissolves mineral scale and calcium buildup inside the unit. Check that vinegar is flowing steadily through both hoses.
6. Clear Away All Vinegar. After the vinegar circulation is complete, replace the vinegar bucket with fresh water and circulate for 15 minutes to remove all vinegar residue. This prevents any lingering taste or odor in your hot water supply.
7. Verify Your Air Pathways. Inspect the intake and exhaust vents for blockages, bird nests, or debris. Clean any obstructions with a soft brush. Ensure vent terminations are properly sealed and that there are no gaps or damage that could affect combustion air flow.
8. Restore and Verify Operation. Remove flushing hoses and reconnect all water lines. Turn on the water supply valves and check for leaks. Restore power and gas supply, then test the unit by running hot water at multiple fixtures to ensure proper operation and temperature.