Boiler runs but radiators or in‑floor loops stay lukewarm or cold

Safety first: Turn off power before working on pumps or zone valves. Use caution with hot water in the system.

• Step 1 – Check boiler temperature setting: Verify the space heating setpoint on the Navien control panel is appropriate (per design). Increase slightly if too low.
• Step 2 – Bleed air from zones: Use purge valves or hose connections on each zone to flush air until a steady stream of water flows. Refill and pressurize the system as needed.
• Step 3 – Verify zone valve operation: Manually open each zone valve (if possible) and feel for hot water entering the loop. Replace any valve that does not open when commanded.
• Step 4 – Check system pump: Ensure the system circulator is running and sized correctly for the connected load. Replace a weak or failed pump.

If heat output remains low, a professional should perform a full hydronic balance and load check.