Medium
E596 on Navien NCB 35 HE

Your boiler has lost its digital connection to your room thermostat, meaning it cannot receive signals to turn the heating on or off.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Communication Error with Smart Room Controller

DIY fix possible

Switch off the power to the boiler at the fused spur or consumer unit.Wait 5 minutes to let the system fully reset.Turn the power back on and check if the thermostat re-establishes its connection with the boiler.

Find a Gas Safe engineer
Search the official register →

Related fault codes

E598View →

Related guides you might find useful

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →