Navien

Navien E016 means the unit’s overheat protection tripped. Scale buildup and restricted flow are the usual suspects — here’s the order to check.

Navien E515 points to a control board (PCB) fault, often tied to grounding or a power surge. Here’s what to check before calling a tech.

Navien E012 means the burner lit, then lost its flame signal mid-cycle. Here’s the diagnosis order, from gas pressure to the flame rod.

Navien E110 means the unit detected abnormal air pressure or an exhaust blockage and shut down safely. Check the filter, vents, and drain.

Navien E003 means ignition failure: the unit couldn’t safely light or detect a burner flame. Check gas supply and the flame rod first.

Every Navien tankless error code with what it means and a link to the full fix. Covers NPE-A2, NPE-S2, and NCB combi boiler series.