Navien E736: cascade communication fault

Larger homes and businesses sometimes link several Navien heaters in a cascade, with one main unit and the others as sub units. The front panel shows which role each unit has. E736 means that link has broken.

The meaning and recommended action below come from Navien's User's Information Manual for NPE-2 condensing water heaters (NPE-180A2, NPE-210A2, NPE-240A2 and the S2 models). Navien technical support: 1-800-519-8794.

Common causes

• A loose, disconnected or damaged communication cable between units
• Wrong main and sub unit settings
• A power problem on one of the units
• A failed control board

What to do

1. Check that every unit in the system has power.
2. Note whether any work was done near the units or their wiring.
3. Call the installer who set up the cascade system; it requires Navien's installation settings.

How to reset it

Navien says you can try resetting the water heater by pressing the Back button on the front panel. If the code returns, the cause is still there and the unit needs service.

Before you call

Have the model number and serial number from the rating plate on the side of the unit ready, along with the date it was installed and the exact code. Navien asks for this information when you contact technical support, and your installer should be your first call for warranty service.

See every code on our Navien error codes page.