How much does it cost to fix Navien error code E736?

Typical repair cost for the Navien E736 fault is £150-300 including labour.

E736 High

Navien E736 Fault Code

Q: What does the Navien E736 fault code mean?

Your boiler is struggling to talk to other linked heating units in your system, meaning it cannot coordinate its operation properly.

The Navien E736 fault code means: your boiler is struggling to talk to other linked heating units in your system, meaning it cannot coordinate its operation properly.. It appears on 4 Navien models in our database.

Technical description: Abnormal operation: cascade communication

Typical repair cost £150-300 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Navien models that show the E736 fault code

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

NCB 28 HE Repair: £150-300
NCB 35 HE Repair: £150-300
NCB 40 HE Repair: £150-300
NCB H Repair: £150-300

Source

Navien E736 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