E783 Medium

Navien E783 Fault Code

The Navien E783 fault code means: your boiler has lost communication with its smart thermostat or remote control unit, preventing it from receiving instructions on when to turn on the heating or hot water.. It appears on 8 Navien models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Abnormal operation: OpenTherm remote control
Typical repair cost £100-250 (including labour)

DIY fix possible

Switch off the power supply to the boiler at the fused spur or circuit breaker.Locate the thermostat or remote controller and check that the wiring connections are secure.Wait 5 minutes for the system to reset, then turn the power back on to see if communication is restored.

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Navien models that show the E783 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Navien E783 fault code information on this page is sourced and cross-checked against the official Navien service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026