High
E594 on Navien NCB CE

Your boiler's internal electronic systems are having trouble talking to each other, which means the device has stopped working to prevent further faults.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Partial PCB communication error

From this model's manual
Verified against the Navien Ncb H installation & service manual, page 78.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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