Navien Error Code E736: CH Return Thermistor Failure
Warning: Your Navien boiler has detected a potential issue with the return water temperature sensor. It's safe to continue using other appliances, but this issue requires professional attention.
How to Fix Navien Code E736
- Check if your boiler is still heating your home. If it is, you can continue using it until a professional can repair it.
- Turn off your boiler if it's not heating your home or if you're not comfortable using it.
- Contact a licensed HVAC technician to diagnose and repair the issue. Do not attempt to repair this yourself.
How to Reset Navien Code E736
- 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 E736 Mean?
The E736 error on your Navien boiler indicates a failure in the return water temperature thermistor. This sensor measures the temperature of the water returning from your heating system. If it's not working correctly, your boiler can't accurately control the water temperature, leading to inefficient heating and potential system damage. This error is typically caused by a faulty thermistor, but it could also be due to a wiring issue or a problem with the boiler's control board.
Common Causes
- Faulty return water temperature thermistor
- Wiring issue between the thermistor and the control board
- Problem with the boiler's control board
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Boiler is not heating | Measure the voltage at the thermistor's terminals using a multimeter | 0V (open circuit) or a voltage reading close to 0V |
| Boiler is heating but showing E736 error | Inspect the wiring between the thermistor and the control board for any signs of damage or corrosion | No damage or corrosion, and all wires are securely connected |
Applicable Navien Models
Source Documentation
Referenced in 5 official Navien technical manuals.
| Manual | Page | Reason | Action |
|---|---|---|---|
| NFB-H Installation & Operation Manual | 116 | Cascade Communication | Check cascade cable. |
| Navien NCB-H Installation & Operation Manual | 130 | Cascade Communication | Contact technical support at 1-800-519-8794. |
| Navien NFB-H Installation & Operation Manual | 116 | Cascade Communication | Check cascade cable. |
| Navien NFC-H Installation & Operation Manual | 128 | Abnormal operation: cascade communication | Alarm |
| Navien NHB-H Installation & Operation Manual | 119 | Cascade Communication | Check cascade cable. |
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Return Water Temperature Thermistor | 7100000003 | — | Find Part |
Related Codes on Same Models
Other codes that affect the same Navien model families as E736.
| 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 |