291Error - Navien NFC-175 Service Manual

5.2.16 291Error

Error conditions and Check Items
Error
E291
Supply / Return inversion limit
Check items
Check method
Fault
Space heating pipe
connection
Version 1.0
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.
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?
Yes
Check the supply and return
temperature sensor
Possible Causes
Defective connection Check whether the space heating pipe connection is inversed.
1. Check the supply temperature sensor connection.
Temperature sensor
2. Check the return temperature sensor connection.
Description
No
Replace space heating pipe
connection
Check method
NFC Service Manual 101