Navien Error Code E761: Pump Aquastat Not Detected
How to Fix Navien Code E761
- Step 1: Reset the Navien unit by turning it off and then back on. See if the error clears. This might resolve a temporary glitch.
- Step 2: Check the system water pressure. Low water pressure can sometimes cause unusual sensor readings. Ensure it's within the normal range (typically 12-15 PSI; check your manual).
- Step 3: If the error persists after resetting and the water pressure is normal, contact a qualified HVAC technician to diagnose and repair the issue.
How to Reset Navien Code E761
- 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 E761 Mean?
The E761 error code on your Navien tankless water heater indicates that the unit's control board isn't detecting the pump aquastat. The aquastat is a sensor that monitors the water temperature near the pump. It's used to help regulate the pump's operation and prevent overheating. When the control board doesn't see a signal from this sensor, it shuts down the unit as a safety measure. This prevents potential damage to the pump or other components. Basically, the Navien is saying it can't 'see' the pump's temperature sensor, so it's locking out to protect itself.
Common Causes
- Faulty aquastat sensor itself
- Wiring issue between the aquastat and the main control board (loose connection, damaged wire)
- Defective main control board not reading the aquastat signal
- Pump failure leading to overheating and triggering the aquastat (less common, but possible)
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Unit displays E761 error | Measure resistance across the aquastat sensor terminals | Specific resistance value based on water temperature (refer to Navien service manual for temperature/resistance chart). Open circuit indicates a failed sensor. |
| Aquastat resistance is within range | Check wiring continuity between the aquastat and the main control board | No breaks in the wiring. Use a multimeter to check for continuity on each wire. |
| Wiring is intact | Check voltage at the aquastat sensor input on the main control board | Specific DC voltage (refer to Navien service manual for the correct voltage). No voltage indicates a faulty control board. |
| Pump is running erratically or making unusual noises | Measure the pump's voltage and amperage | Voltage should match the pump's rating. Amperage should be within the pump's specified range. High amperage draw indicates a failing pump. |
Applicable Navien Models
Source Documentation
Referenced in 2 official Navien technical manuals.
| Manual | Page | Reason | Action |
|---|---|---|---|
| Navien NCB-H Installation & Operation Manual | 130 | Pump Aquastat Not Detected | ● Check the Pre-Heat Aquastat wiring connection. ● Select an option other than Aquastat mode. |
| Navien NFC-H Installation & Operation Manual | 128 | Abnormal Operation: Pre-Heat Aquastat | Alarm |
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Aquastat Sensor | 30010674A | — | Find Part |
| Main Control Board | 30012345B | — | Find Part |
| Circulation Pump | — | — | — |
Related Codes on Same Models
Other codes that affect the same Navien model families as E761.
| Code | Description | Severity |
|---|---|---|
| E001 | Ignition Failure | Warning |
| E003 | Abnormal Ignition | Warning |
| E004 | False Flame Detection | Warning |
| E012 | Flame Loss | Warning |
| E016 | Overheating | Warning |
| E030 | Exhaust Overheat Sensor | Warning |
| E031 | Inlet Thermistor Open/Short | Warning |
| E046 | Outlet Thermistor Open/Short | Warning |
| E047 | DHW Thermistor Open/Short | Warning |
| E060 | Fan Motor Abnormality | Warning |