Navien furnace runs but does not provide enough heat to the home; supply water temperature is lower than expected

Safety: Turn off power before adjusting internal settings or opening panels. Hydronic water can be hot; use caution.

• Check thermostat and setpoint: Verify that the room thermostat is calling for heat and that the Navien's target supply temperature is set appropriately for the system type (radiant, baseboard, etc.).
• Review outdoor reset settings: If using outdoor reset, enter the installer menu and check the heating curve. Increase the slope or shift slightly according to the manual to raise water temperature during cold weather.
• Bleed air from system: Air pockets reduce heat transfer. Use air vents and bleeders on radiators or manifolds to purge air while the circulator is running. Top up system pressure as needed.
• Check circulator sizing and speed: If the system uses a variable-speed pump, ensure it is not set to a very low speed. For fixed-speed pumps, confirm the pump model meets the required flow and head for the system. Replace with a properly sized pump if necessary.
• Inspect balancing valves: Ensure manifold or zone balancing valves are not partially closed, restricting flow to key areas. Adjust as needed to restore proper circulation.