Navien Water Heater Pilot Won’t Stay Lit — What’s Happening
Navien tankless water heaters do not have a standing pilot light. They use electronic ignition to light the burner on demand. When someone says the pilot won’t stay lit, the unit is actually failing to ignite or losing flame after ignition. This typically appears as Error 11 (ignition failure, where the unit tried to light but did not detect flame) or Error 12 (flame failure, where the burner lit but the control board lost the flame signal and shut down the gas valve).
The control board relies on a flame rod sensor to prove that combustion is happening. If the sensor cannot detect flame, the gas valve closes immediately for safety. The result is a burner that lights briefly and then goes out, or fails to light at all. This behavior mimics an old-style pilot that won’t stay lit, but the actual problem is in the ignition sequence, flame detection circuit, gas delivery, or combustion air supply.
Most Likely Causes
- Dirty or contaminated flame rod sensor Buildup on the flame rod prevents reliable flame detection, so the control board shuts down the gas valve even though the burner is actually lit.
- Inadequate gas supply or gas valve not opening fully Gas shutoff valve not fully open, low gas pressure at the meter, or a failing gas valve will prevent ignition or cause the flame to drop out immediately.
- Igniter or electrode dirty, misaligned, or damaged Dirt, soot, corrosion, or physical damage on the igniter or electrode assembly prevents reliable spark or flame establishment.
- Blocked intake filter or exhaust vent Restricted combustion air or exhaust flow starves the burner of oxygen or prevents stable flame, triggering flame-failure shutdown.
- Faulty flow sensor causing shutdowns A flow sensor that does not spin properly can cause the unit to shut down in ways that mimic ignition or flame failure.
- Loose wiring or damaged connectors at ignition components Poor electrical connections to the igniter, flame rod, or gas valve interrupt the ignition sequence or flame-sensing circuit.
- Failed control board If the control board cannot process flame-detection signals or command the gas valve properly, the unit will fail to light or drop flame even when all hardware is clean and connected.
How to Diagnose and Fix
- Check the display for an error code (most commonly Error 11 or Error 12) to confirm the fault is ignition or flame failure, not another system problem.
- Verify the gas supply by confirming all manual gas shutoff valves upstream of the unit are fully open and that other gas appliances in the home are working normally.
- Inspect the intake air filter and combustion air path for blockage, lint, or debris and clean or replace the filter if dirty.
- Remove and inspect the flame rod and igniter assembly for soot, corrosion, cracks, or misalignment and clean gently with fine abrasive pad or replace if damaged.
- Check all wiring and connectors to the igniter, flame rod, and gas valve for looseness, corrosion, or visible damage and reseat or repair as needed.
- If the unit lights briefly and then shuts down, clean the flame rod thoroughly and test again to see if flame proving now succeeds.
- If the fault persists after cleaning and the gas supply is confirmed good, consider testing the flow sensor by briefly opening and closing the pressure relief valve near the unit outlet, then call for professional diagnostics.
- If all hardware checks pass and the error continues, the gas valve or control board likely needs replacement and should be diagnosed by a qualified technician or Navien service specialist.
Parts You Might Need
| Part | Notes |
|---|---|
| Flame rod sensor assembly | Amazon | Detects burner flame; often fouled by combustion deposits |
| Igniter / ignition electrode | Amazon | Creates spark to light gas; can crack, corrode, or misalign |
| Gas valve | Amazon | Controls gas flow to burner; may fail to open or modulate |
| Control board (PCB) | Amazon | Manages ignition sequence and flame detection; replace if logic faults persist |
When to Call a Pro
Gas appliance ignition and flame-detection work involves live gas lines, high-voltage ignition circuits, and precise combustion tuning. If basic cleaning of the flame rod and igniter does not resolve the fault, or if you are not comfortable working with gas connections and electrical components, call a licensed technician or a Navien service specialist. Navien recommends that unresolved faults, especially those involving the gas valve, control board, or flow sensor, be diagnosed by the original installer or an authorized service provider. Incorrect repairs can create safety hazards or void warranty coverage. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.