Navien Tankless & Boiler Certified Service Specialist

These are ‘ignition failure’ or ‘false flame detection’ codes. While they can indicate a gas supply issue, in our experience they are almost always caused by a lack of maintenance. A clogged condensate trap or neglected neutralizer can back up the system and prevent ignition. Annual maintenance prevents this.

E110 indicates ‘abnormal air pressure’ or an exhaust blockage. This often happens if the intake air filter is clogged with dust or lint, or if the exhaust venting is obstructed. Check your air filter first — if the issue persists, a technician needs to inspect the venting system.

Navien recommends annual maintenance. This includes cleaning the inlet water filter, cleaning the air intake filter, and flushing the heat exchanger with a descaling solution. Descaling is critical in hard water areas — Marin County water is particularly hard and accelerates scale buildup.

A leak can come from the unit itself or the connections. Common sources are the condensate trap (if cracked or loose) or the pressure relief valve (if system pressure is too high). If you see water, turn off the supply to the unit and call a technician immediately — don’t wait.

E012 is ‘Flame Loss’ — the burner lit successfully but the flame went out during operation. This is commonly caused by low gas pressure, a dirty flame rod, or wind blowing into the exhaust vent. Check that no other gas appliances are running simultaneously (gas pressure drop). If E012 keeps recurring, a technician needs to check gas pressures and clean the flame rod. Schedule a service call.

E515 indicates ‘Low Water Flow’ — the unit is not getting enough water to operate safely. Common causes include a clogged inlet filter, partially closed supply valves, or scale buildup in the heat exchanger restricting flow. Start by checking the inlet filter (you can clean it yourself). If the filter is clean, the heat exchanger likely needs descaling — especially in hard water areas like Marin County.

E594 means ‘Condensate Blockage’ — the condensate drain system is backed up. All condensing Navien units produce acidic condensate that must drain freely. If the condensate trap, drain line, or neutralizer cartridge is clogged, the unit shuts down as a safety precaution. A technician needs to clear the blockage and flush the condensate system. This is one of the most preventable codes — annual maintenance includes condensate system inspection.

E016 is an ‘Overheating’ safety shutdown. The unit’s outlet water temperature exceeded safe limits. This usually means the system pump has failed or is running too slowly, the heat exchanger is heavily scaled, or there’s an air lock in the system. Do not attempt to reset repeatedly — overheating can damage the heat exchanger. Call a technician to diagnose the root cause.