Nov 27, 2022 · What Does Navien E438 Error Code Mean? Navien E438 Error Code means the circulation pump is operating abnormally. Several things like a check valve, flow sensor, and pump …

Nov 14, 2025 · Navien E438 error fix: diagnose critical overheating. Learn safe troubleshooting steps and when professional venting or scaling repair is necessary.

Aug 24, 2023 · The E438 error code, indicating recirculation pump or flow control issues, affects 8-12% of Navien tankless water heaters with integrated or external recirculation systems during their lifespan.

Mar 27, 2024 · What causes Navien error code E438? The most common reason is not fully opening all the water lines. Find out all you need to know to solve this code.

Jul 11, 2025 · In this comprehensive tutorial, we will guide you through the process of fixing the Navien E438 error code, commonly known as the cold water sandwich error. ...

Sep 16, 2025 · What it Means: These codes all indicate a failure of a temperature sensor (thermistor) on the closed-loop heating side of your combi-boiler. The system cannot accurately read the water …

May 21, 2024 · Each time the circuit breaker was reset, the Navien flashed error E438. I replaced two AFCI breakers that were constantly tripping, which did mitigate the tripping, but it happened again, …

To troubleshoot the E.438 code on your Navien boiler, first inspect the vent pipe for obstructions like nests or debris. Check the air intake for blockages that restrict airflow. Clean or clear any visible …

Learn how to fix Navien error code E438. Display shows E438; unit may not modulate or control temperature correctly.. See common causes and step-by-step DIY repair instructions.

Nov 23, 2025 · Diagnose and clear Navien Error Code 438. Understand the root cause of the safety shutdown and get your hot water back.