Navien Error Code E805: Abnormal supply air- temp sensor operation for lower limit

How to Fix Navien Code E805

1. Step 1: Check that your incoming water supply is turned on fully. A partially closed valve could affect the temperature reading.
2. Step 2: If the weather is extremely cold, ensure that pipes are not frozen. Frozen pipes can cause unusual temperature readings.
3. Step 3: Reset the unit by turning off the power at the breaker for 30 seconds, then turn it back on. This may clear a temporary error.
4. Step 4: If the error persists after these steps, contact a qualified HVAC technician to diagnose and repair the issue.

How to Reset Navien Code E805

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 E805 Mean?

The E805 error code on your Navien tankless water heater indicates that the unit is detecting an abnormal reading from the supply water temperature sensor, specifically related to a lower limit threshold. This sensor is responsible for monitoring the temperature of the incoming cold water entering the unit. The Navien's control board uses this information to regulate the burner and maintain the desired output water temperature. If the sensor malfunctions or provides an incorrect reading, the unit may shut down as a safety measure to prevent overheating or other potential issues. Essentially, the control board is seeing a supply water temperature that is outside of the expected range. This could be due to a faulty sensor, wiring problems, or even unusually cold incoming water. Because the unit can't reliably determine the incoming water temperature, it locks out to prevent potential damage or unsafe operation. This error will prevent you from getting hot water until the issue is addressed.

Common Causes

• Faulty supply water temperature sensor (thermistor)
• Loose or corroded wiring connections to the supply water temperature sensor
• Wiring harness damage between the sensor and the main control board
• Defective main control board (rare, but possible)
• Extremely cold incoming water temperature (rare, but possible in certain climates)

Diagnostic Steps

Replacement Parts

Related Codes on Same Models

Other codes that affect the same Navien model families as E805.