Scale from hard water builds up inside a tankless heat exchanger, restricting flow and shortening the unit's life. With San Diego water averaging about 16 grains per gallon, this maintenance matters more here than in soft-water areas.
Safety first
Turn off the power and gas to the unit before descaling. Navien notes that incorrect descaling may void the warranty and recommends a professional; follow your model's manual.
Rinnai's guidance
- Flush at least once a year.
- Use 4 gallons of undiluted white vinegar.
- Never use chemical solutions of any kind.
- Turn off power and gas first.
Navien's guidance
- Descale at least yearly, with a commercial descaler or white vinegar.
- Circulate the solution for 45 minutes or more.
- Flush with fresh water for 10 minutes or more.
- Incorrect descaling may void the warranty; a professional is recommended.
What you need
A descaling kit is a small submersible pump, two hoses and a bucket, connected to the isolation (service) valves on the heater's water lines. If your heater has no service valves, have a plumber add them; they make every future flush easy.
Common questions
How often should I descale in San Diego?
At least yearly per Rinnai and Navien. In hard water, more often helps; ask your installer to suggest a schedule for your unit.
Do I need a water softener for tankless?
Some manufacturers require water treatment in hard-water areas to keep the warranty. Check your model's manual and warranty terms.
General information, not professional or legal advice; follow your manufacturer's manual, and your installer and local permit office have the final word. Sources:Rinnai, Flushing my Rinnai tankless water heater; Navien, How to descale tankless water heaters; U.S. Department of Energy, Building America: Transitioning to a Tankless Water Heater; City of San Diego, Water Quality (hardness).
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