Water is warm but not hot enough even when the Navien setpoint is at maximum; no error code displayed.

Safety: Avoid setting temperatures above safe levels (typically 120–125°F / 49–52°C) to prevent scalding.

Steps:

• 1. Verify set temperature: Check the Navien front panel or remote controller to confirm the DHW setpoint. Ensure any child-lock or max-temp limit settings are not restricting temperature.
• 2. Check for crossover: Turn OFF the cold water supply to the Navien. Open a hot water tap; if water still flows strongly, there is a crossover (e.g., faulty single-handle faucet or mixing valve) allowing cold water into the hot line. Identify and repair the offending fixture.
• 3. Descale heat exchanger: If the unit is older or in a hard water area, flush the heat exchanger to restore full heating capacity.
• 4. Check flow rate: Extremely high flow (multiple fixtures) may exceed the unit's capacity; reduce simultaneous demand and see if temperature improves.

If water remains lukewarm after these steps, the outlet thermistor or gas valve modulation may require professional diagnosis.