Navien Error Code E438: Navien Error Code E438 - Abnormal Operation

Severity
Warning
Type
digital display
Estimated repair cost: $75 — $200 (parts + labor)
Warning: Your Navien tankless water heater or combi-boiler has detected an abnormal operation and has likely locked out. This requires investigation to restore hot water and/or heating.

How to Fix Navien Code E438

  1. Step 1: Reset the unit by turning off the power switch for 5 minutes, then turn it back on. See if the error clears.
  2. Step 2: Check the incoming water pressure to the unit. Ensure it meets the minimum requirement specified in your Navien manual.
  3. Step 3: Inspect the exterior vent for any obvious obstructions like leaves, snow, or debris. Clear any blockages you can safely reach.
  4. Step 4: If the error persists after these steps, contact a qualified HVAC technician to diagnose and repair the unit.

How to Reset Navien Code E438

  1. Turn off the unit using the power button on the front panel.
  2. Turn off the gas supply valve.
  3. Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
  4. Restore power at the breaker, then open the gas valve.
  5. Turn the unit back on. If the error returns, the underlying issue needs repair.

Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.

What Does Navien Error Code E438 Mean?

The Navien error code E438 indicates that the unit has detected an abnormal operation. This is a broad error code that essentially means the unit's control board has sensed something is not right during its normal operation. It could be related to combustion, water flow, or other sensor readings falling outside acceptable parameters. The unit will likely shut down as a safety measure. This code is often triggered by a temporary issue but can also point to a more serious underlying problem that needs professional attention. Because this is a broad error, further diagnostics are needed to pinpoint the root cause.

Common Causes

  • Temporary sensor glitch or electrical noise causing a false reading.
  • Combustion issues: improper gas pressure, blocked vent, or faulty burner.
  • Water flow problems: low water pressure, blocked inlet filter, or malfunctioning flow sensor.
  • Faulty or miscalibrated sensors (temperature, pressure, or flow).
  • Condensate blockage preventing proper drainage.

Diagnostic Steps

If... Check Expected
Unit displays E438 after reset Check gas supply pressure at the unit's gas valve while the unit attempts to fire Within the range specified on the unit's nameplate (typically 4-7" WC for natural gas, 10-13" WC for propane)
Gas pressure is within range Inspect the combustion blower motor and venturi for obstructions or damage Blower operates smoothly and venturi is clear
Blower and venturi are OK Measure the resistance of the APS (Air Pressure Switch) with the blower off and on Open circuit with blower off, closed circuit with blower on
APS switch functions correctly Check the inlet water filter for debris Filter is clean and free of obstructions

Applicable Navien Models

Replacement Parts

Part OEM Number Est. Cost Where to Buy
Air Pressure Switch (APS) 30010687A — Find Part
Flow Sensor 30011812A — Find Part
Gas Valve — — —

Related Codes on Same Models

Other codes that affect the same Navien model families as E438.

Code Description Severity
E001 Ignition Failure Warning
E003 Abnormal Ignition Warning
E004 False Flame Detection Warning
E012 Flame Loss Warning
E016 Overheating Warning
E030 Exhaust Overheat Sensor Warning
E031 Inlet Thermistor Open/Short Warning
E046 Outlet Thermistor Open/Short Warning
E047 DHW Thermistor Open/Short Warning
E060 Fan Motor Abnormality Warning