Water temperature fluctuates between hot and cold during a shower with no error code.

Safety: Turn off power and gas before servicing. Water may be hot; use caution.

• Check plumbing fixtures: If using a thermostatic or pressure-balancing shower valve, test with a simple manual mixer to rule out fixture issues.
• Inspect and clean heat exchanger: If scale is suspected (hard water area), flush the DHW heat exchanger with an approved descaling solution.
• Verify sensors: Test the DHW outlet temperature sensor and flow sensor for correct operation and replace if readings are unstable.
• Check minimum flow: Ensure that the flow rate at the fixture meets the heater's minimum activation flow. Very low flow can cause cycling.
• Test operation: After cleaning and sensor checks, run a continuous draw and confirm stable temperature.