Takagi unit shuts down with error 103; water temperature may fluctuate before shutdown.

Safety first: Turn OFF power and gas. Allow the heater to cool. Close the cold and hot isolation valves before disconnecting any plumbing. Wear gloves and eye protection when handling descaling chemicals.

Steps:

• 1. Check inlet water filter: Close the cold water isolation valve. Remove the cold inlet filter screen (usually at the cold inlet connection). Rinse under running water and brush off debris. Reinstall and open the valve.
• 2. Verify isolation valves: Ensure both hot and cold isolation valves to the heater are fully open during normal operation.
• 3. Descale the heat exchanger:
  • Connect a tankless water heater flush kit (pump, hoses, and bucket) to the service ports on the hot and cold lines.
  • Fill the bucket with white vinegar or a manufacturer-approved descaling solution.
  • Open the service valves and run the pump to circulate solution through the heater for 45–60 minutes.
  • After flushing, drain the solution, then flush with clean water for 5–10 minutes.
• 4. Inspect flow sensor: With water off and unit cool, remove the flow sensor assembly (usually on the cold inlet side). Check for debris or scale on the turbine/impeller. Clean gently and reinstall.
• 5. Restore service: Open all valves, restore power and gas, and test hot water. If error 103 returns, the heat exchanger may be severely scaled or damaged and may require replacement by a technician.