Navien Error Code E799: Leak detected (sensor)
How to Fix Navien Code E799
- Step 1: Check around the outside of the unit for any obvious signs of water leakage. Look at the pipe connections and the floor around the unit.
- Step 2: Ensure the unit's condensate drain line is properly connected and not blocked. A clogged drain can cause water to back up.
- Step 3: If you see any significant amount of water or can't identify the source, contact a qualified HVAC technician to diagnose and repair the leak.
How to Reset Navien Code E799
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Navien Error Code E799 Mean?
The Navien E799 error code indicates that the unit's leak detection sensor has been triggered. Navien tankless water heaters have sensors designed to detect moisture in areas where it shouldn't be, like inside the sealed burner compartment or around sensitive electronics. When the sensor detects water, the unit shuts down as a safety precaution to prevent further damage. This isn't necessarily a catastrophic failure, but it does mean that water is present where it shouldn't be, and the source of the leak needs to be identified and fixed. Ignoring this error could lead to corrosion, electrical damage, or even more serious component failures down the road.
Common Causes
- Internal leak within the heat exchanger.
- Loose plumbing connections inside the unit.
- Condensation buildup due to poor venting or excessive humidity.
- Faulty leak detection sensor.
- Damaged or leaking internal components like pumps or valves.
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Unit displays E799 error | Inspect the heat exchanger for signs of leaks or corrosion. | No visible leaks or corrosion. |
| No visible heat exchanger leak | Check all internal plumbing connections (especially around pumps and valves) for tightness and signs of leaks. | All connections are tight and dry. |
| Connections are tight | Measure the resistance of the leak detection sensor. Refer to the Navien service manual for the correct value. | Resistance within specified range. |
| Sensor resistance is out of range | Replace the leak detection sensor. | Error code clears after replacement. |
Applicable Navien Models
Source Documentation
Referenced in 1 official Navien technical manual.
| Manual | Page | Reason | Action |
|---|---|---|---|
| Navien NPF Installation & Operation Manual | 128 | Leak detected (sensor) | This error occurs when a leak occurs in the furnace. ● Open the lower-front cover and check for leaks in the furnace. ● If you find any leaks in the furnace, contact Technical Support at 1-800-519-8794. |
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Leak Detection Sensor | 30014522A | — | Find Part |
| Heat Exchanger Assembly | — | — | — |
| Condensate Drain Assembly | — | — | — |
Related Codes on Same Models
Other codes that affect the same Navien model families as E799.
| Code | Description | Severity |
|---|---|---|
| E001 | Ignition Failure | Warning |
| E003 | Abnormal Ignition | Warning |
| E004 | False Flame Detection | Warning |
| E031 | Inlet Thermistor Open/Short | Warning |
| E046 | Outlet Thermistor Open/Short | Warning |
| E110 | Exhaust Blocked | Warning |
| E205 | Water Flow Sensor Failure | Warning |
| E517 | Water Flow Switch Failure | Warning |
| E736 | CH Return Thermistor Failure | Warning |
| E740 | CH Buffer Tank Thermistor | Warning |