Navien Error Code E517: Water Flow Switch Failure
How to Fix Navien Code E517
- Step 1: Check the system pressure gauge on the front of the unit. It should read between 12 and 25 psi. If below 12 psi, open the fill valve to repressurize to 15 psi. Do not exceed 25 psi.
- Step 2: Try pressing the 'Reset' button on the control panel for 3 seconds to clear the lockout. If the error returns immediately, proceed to step 3.
- Step 3: If the pressure is fine and reset doesn't work, call a qualified HVAC technician. Do not open the unit—there are live electrical connections and gas components inside.
How to Reset Navien Code E517
- 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 E517 Mean?
The E517 error on your Navien boiler or water heater means the water flow switch did not close within 10 seconds after a call for heat or hot water. The flow switch is a safety device that confirms water is actually moving through the heat exchanger before the burner fires. If the switch doesn't close, the unit locks out to prevent overheating or damage to the heat exchanger. This is commonly caused by a stuck or failed flow switch, but can also happen when the system is low on water pressure, has air trapped in the pipes, or the pump isn't running. Some Navien models use a magnetic reed switch; others use a Hall effect sensor. On combi units (NCB), the internal circulator must be running for flow to occur. On tankless water heaters (NPE, NPN), the flow switch is triggered by the pressure drop across an internal orifice when a hot water tap is opened. You'll need to check the system pressure, bleed air from the unit and zone piping, and verify the pump is getting power. If those are all fine, the flow switch itself is likely defective and needs replacement.
Common Causes
- Defective or stuck flow switch (reed switch stuck open, or paddle stuck from debris)
- Low system water pressure below 12 psi (boiler) or blocked supply filter (tankless)
- Air trapped in heat exchanger or pump head preventing water flow
- Failed internal or external system circulator pump (no movement/flow)
- Wiring issue or loose connection at flow switch harness
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| System pressure gauge reads below 12 psi | Pressurized water supply and auto-fill valve. Check for leaks in pipes or relief valve. | 15–20 psi at all times when cold system is full |
| Pressures are normal, but you hear the pump humming and no water flow | Air purger or automatic air vent on top of the unit. Listen for gurgling in the pipes. | No air hissing, steady water flow sound |
| No pump noise at all when a call for heat/hot water is active | Voltage at pump terminals (typically 120V) using a multimeter | 120 VAC between L and N terminals when call is active |
| Pump runs but the flow switch still doesn't close | Flow switch resistance with a multimeter. On NCB models, check reed switch continuity. | 0 Ω (closed) when flow is present; infinite Ω (open) when no flow |
Applicable Navien Models
Source Documentation
Referenced in 6 official Navien technical manuals.
| Manual | Page | Reason | Action |
|---|---|---|---|
| NFB-H Installation & Operation Manual | 116 | Abnormal DIP Switch | Check DIP switch settings. |
| Navien NCB-H Installation & Operation Manual | 130 | Abnormal DIP Switch | Contact technical support at 1-800-519-8794. |
| Navien NFB-H Installation & Operation Manual | 116 | Abnormal DIP Switch | Check DIP switch settings. |
| Navien NFC-H Installation & Operation Manual | 127 | Abnormal operation: Dip switch setting | Manual RESET |
| Navien NHB-H Installation & Operation Manual | 119 | Abnormal DIP Switch | Check DIP switch settings. |
| Navien NPF Installation & Operation Manual | 127 | Abnormal DIP switch settings | This error occurs when the furnace’s capacity does not match with the main controller. ● If this error occurs continuously, contact Technical Support at 1-800-519-8794 |
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Flow Switch Assembly (Reed Switch) | NAV-30031974B | — | Find Part |
| Water Flow Sensor (Hall Effect) | NAV-30025068A | — | Find Part |
| Internal Circulator Pump | — | — | — |
Related Codes on Same Models
Other codes that affect the same Navien model families as E517.
| 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 |