Green Flow Solution logo
Schedule Service

Troubleshooting code

Back to all NWP500 Series error codes

Navien NWP500 Series E990 troubleshooting

Abnormal safety or control operation. Use this page to document the issue and prepare for service. GreenFlow should handle diagnosis for electrical, refrigerant, lockout, or recurring conditions.

Schedule Service +1 (857) 767-6414

What the code means

E990: Abnormal safety or control operation

The Navien manual for this product family lists E990 as: Abnormal safety or control operation.

System area
Equipment control
Service level
Service recommended

Safe checks before calling

  • Record the exact Navien code, whether the unit is locked out, and when the code appeared.
  • Confirm thermostat, controller, or front-panel status without changing service settings.
  • Check only visible intake, exhaust, filter, clearance, condensate, and water-supply conditions that can be inspected without opening panels.
  • Take photos of the code, equipment nameplate, venting, surrounding equipment area, thermostat or controller, and any visible leak, ice, or obstruction.

When to stop and call GreenFlow

Call GreenFlow if the code repeats, the unit is locked out, hot water, heating, or cooling is not restored, or the concern involves gas, flame, combustion, venting, electrical components, refrigerant, pressure, water leaks, PCB/control boards, sensors, pumps, or warranty coverage.

Share the visible code, model and serial number if available, photos, current symptoms, and whether the issue affects heating, cooling, or both.

E990 questions

What does E990 mean on a Navien NWP500 Series?

The Navien manual for this product family lists E990 as: Abnormal safety or control operation.

What should I safely check before scheduling service?

Record the displayed code, confirm thermostat or controller status, check only visible intake, exhaust, filter, clearance, and water-supply conditions, and take photos of the code and nameplate. Do not open gas, electrical, refrigerant, combustion, or internal equipment panels.

When should GreenFlow handle this code?

Call GreenFlow if the code repeats, the unit is locked out, hot water, heating, or cooling is not restored, or the concern involves gas, flame, combustion, venting, electrical components, refrigerant, pressure, water leaks, PCB/control boards, sensors, pumps, or warranty coverage.

Need help with this code?

GreenFlow can review the code, photos, equipment access, and symptoms before scheduling the right next step.

Schedule Service Back to product

Brands We Service

Popular cities

Service Areas

Our Happy Customers

Ray

Just had a service call because my tankless water heater stopped working with E110 code. Andrey located the root cause real quick and fixed the issue within half an hour, also gave reasonable recommendations for further maintenance.

Jack B.

Andrey always does a great job.

Neal V.

In an industry that often fraught with contractors taking advantage of homeowners, Andrey was honest with his assessment and willing to install a product acquired elsewhere (most want that margin themselves), patiently answered my questions (I’m an engineer so like to understand what’s happening), and proactively offered practical...

Randy J.

Thanks to Andrey for an amazingly quick response to my request for a service call. He diagnosed and fixed my issue within 24 hours of my asking for help. Excellent service. Thanks.

View All