Name: Navien NHB-110
Brand: Navien
Rating: 4 (1 reviews)

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114 NHB Service Manual

Version 1.0

5.2.17 291Error

Error conditions and Check Items

Error Description

E291

Supply / Return inversion limit

If the return temperature is higher than “supply temperature + 10°F (5.5°C)”, the system stops

operation and displays error code (E291) on the front panel.

Check items

1. Check whether the space heating pipe connection is inversed.

2. Check the supply temperature sensor connection.

3. Check the return temperature sensor connection.

Is the space heating pipe

connection normal?

Check the supply and return

temperature sensor

Replace space heating pipe

connection

Yes

Check method

Fault Possible Causes Check method

Space heating pipe

connection

Defective connection Check whether the space heating pipe connection is inversed.

Temperature sensor

1. Check the supply temperature sensor connection.

2. Check the return temperature sensor connection.

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