Navien NFC-175 Installation & Operation Manual page 102

Error Code Reason
E615 Abnormal operation: input and memory
E736 Abnormal operation: cascade communication
Abnormal operation: outdoor temperature sensor
E740 (appears only when the outdoor reset curve is
enabled).
E761 Abnormal operation: Pre-Heat Aquastat
E777 LWCO (service code: 7700) (external device)
E782 Abnormal operation: main panel communication
Abnormal operation: zone controller
E784
communication
If any of these remedies do not resolve the problem, contact Technical Support at 1-800-519-8794.
102 Operating the Boiler
Self-Diagnostic/ Action
Contact technical support at 1-800-519-8794.
Contact technical support at 1-800-519-8794.
Ensure that the outdoor reset curve is configured properly.
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Check the outdoor temperature sensor wiring connection.
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Check the Pre-Heat Aquastat wiring connection.
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Select an option other than Aquastat mode.
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Check the LWCO wiring connection.
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Ensure that the system water level is appropriate.
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Add make-up water to the system if necessary.
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Contact technical support at 1-800-519-8794.
Contact technical support at 1-800-519-8794.