Descale Tankless Water Heater

If you have a tankless (on-demand) water heater, this task replaces the standard 'Flush Water Heater' task. Unlike tank-style heaters, tankless units develop mineral scale on the heat exchanger — in hard water areas, just one year of buildup can reduce efficiency by 25% and trigger error codes. Descale annually (every 6 months in very hard water areas). You'll need a submersible pump, two washing machine hoses, a 5-gallon bucket, and food-grade white vinegar or a commercial descaler like Rheem or Navien's recommended product. Step 1: Close the hot and cold service valves on the heater. Step 2: Connect hoses to the service ports (cold in, hot out). Step 3: Put both hose ends in a bucket with 2–3 gallons of undiluted white vinegar. Step 4: Run the submersible pump to circulate vinegar through the heat exchanger for 45–60 minutes. Step 5: Flush with fresh water for 5–10 minutes to clear all vinegar. Step 6: Close service ports, reopen service valves, and restore power. Check manufacturer instructions for your specific model — many manufacturers (Rinnai, Navien, Rheem) have YouTube videos showing this exact process for their units. A descaled unit should fully restore efficiency and eliminate error code E10/E11 (flow errors often caused by partial scale blockage).