Navien Tankless Water Heater Not Heating Water: Fix It Now

Navien Tankless Water Heater Not Heating Water: Fix It Now

Tankless water heaters have become a staple in modern HVAC systems, with Navien leading the way in innovation and performance. Designed for efficiency and convenience, these units deliver hot water on demand without the need for bulky storage tanks. However, when your Navien tankless water heater stops heating water, it can bring your household to a standstill. Whether the issue stems from faulty Navien parts or system errors, quick troubleshooting is key. In this article, we’ll explore the most common causes of this problem and how to fix them, so you can get your hot water flowing again fast.

Common Causes and Fixes for Navien Tankless Water Heater Not Heating Water

Here are the most common causes and quick fixes for when your Navien tankless water heater isn’t heating water.

Low or Inadequate Water Flow

Navien tankless water heaters require a minimum flow rate to activate the burner and begin heating. If water flow is too low, whether due to fixtures being only partially open or mineral buildup in pipes, the system will not detect the demand for hot water and will fail to heat.

Fixes:

• Ensure Water Valves are Fully Open: Check all water supply valves connected to the tankless water heater, especially the hot and cold inlets, and make sure they are fully open to allow maximum flow.

• Clean Aerators and Showerheads: Over time, sediment and minerals can clog the aerators on faucets and showerheads. Clean them to improve water flow.

• Check Home Water Pressure: The water pressure in your home should be above 30 PSI for optimal performance. If it's lower, this could be the reason your unit isn't heating properly.

• Inspect the Flow Sensor: The flow sensor detects water movement and signals the burner to ignite. If the sensor is faulty, it may need to be cleaned or replaced with genuine parts.

  
  

Clogged Cold Water Inlet Filter

Navien systems are equipped with a mesh filter on the cold water inlet, designed to block debris from entering the system. Over time, this filter can become clogged with dirt, scale, and mineral deposits, restricting water flow and preventing the unit from heating.

Fixes:

• Turn Off Power and Water Supply: Before servicing the unit, ensure the water supply and electrical power to the system are turned off.

• Clean the Inlet Filter: Remove the cold water inlet filter and rinse it under warm water. For stubborn mineral buildup, soak the filter in vinegar to dissolve deposits.

• Reinstall the Filter: Once the filter is cleaned, reinstall it and check if the unit is heating properly.

  
  

Ignition Failure 

An ignition failure occurs when the unit tries to ignite the gas burner but fails. This can be caused by gas line obstructions, a faulty igniter, or issues with the control board that prevent ignition from occurring.

Fixes:

• Open the Gas Valve: Ensure the gas valve is fully open to allow gas to flow into the unit.

• Check for Gas Leaks or Low Gas Pressure: Inspect the gas lines for leaks and ensure the gas pressure is sufficient for the unit to operate.

• Inspect and Clean the Igniter: The igniter can become dirty or corroded over time. Clean it or replace it with OEM Navien parts if it shows signs of damage.

• Reset the System: After cleaning or replacing the igniter, reset the system and attempt to restart it.

Pro Tip:

If ignition failures are frequent, it's advisable to call a certified HVAC technician to inspect the gas pressure and combustion chamber for further issues.

Blocked Venting or Air Intake 

Navien tankless water heaters require proper ventilation to ensure safe combustion. If the intake or exhaust vent becomes blocked, the system may overheat, shut down, or fail to ignite.

Fixes:

• Clear Vent Blockages: Inspect the intake and exhaust vent pipes for obstructions such as leaves, bird nests, or snow buildup. Clear these blockages to allow proper airflow.

• Clean or Replace the Intake Filter: Some Navien units feature air intake filters that should be cleaned or replaced periodically.

• Ensure Proper Vent Slope: Check that the vent pipes are sloped and installed according to installation guidelines.

  
  

Mineral Scale in the Heat Exchanger

Hard water can lead to the buildup of calcium and lime deposits inside the heat exchanger, reducing heat transfer efficiency. Over time, this mineral scale buildup can cause the system to overheat and potentially block water flow entirely.

Fixes:

• Shut Off Power and Water: Turn off the power supply and water flow to the unit before beginning maintenance.

• Use a Descaling Solution: Connect a flushing kit to the service ports of the unit and circulate a descaling solution (e.g., vinegar or a Navien-approved chemical) through the heat exchanger for 45 to 60 minutes.

• Flush with Clean Water: After descaling, flush the system thoroughly with clean water to remove any remaining solution.

• Restart the Unit: Once the flushing process is complete, restart the unit and check if the water heater is functioning correctly.

  
  

Preventative Tip:

Install a water softener or use Navien’s scale prevention system to reduce mineral buildup. Regular flushing every 6-12 months is especially important in areas with hard water.

Defective Flow Sensor

The flow sensor detects water movement and signals the burner to ignite. If the sensor becomes clogged, dirty, or damaged, it may fail to activate the burner, resulting in no hot water.

Fixes:

• Clean the Flow Sensor: If the sensor is dirty, clean it gently with a soft brush and descaling agent.

• Replace the Sensor: If cleaning doesn’t solve the problem, replace the defective flow sensor with a genuine Navien part.

• Test the System: After replacing the sensor, reset the system and check if the unit is heating water properly.

  
  

Tripped High-Limit Switch or Overheat Cutoff

The high-limit switch is a safety feature designed to shut down the unit if the internal temperature exceeds safe limits, typically due to issues like restricted water flow or poor ventilation.

Fixes:

• Allow the Unit to Cool Down: If the high-limit switch has tripped, wait for the unit to cool down before resetting the switch.

• Identify Overheating Causes: Check for causes of overheating, such as mineral scale buildup, venting issues, or a malfunctioning thermostat.

• Replace Defective Components: If the switch continues to trip, consider replacing the thermistor or control board, particularly if the unit is older.

Pro Tip:

Regular maintenance can prevent the high-limit switch from tripping frequently. This includes cleaning components and checking for system imbalances.

Flame Loss During Operation

The flame loss error indicates that the burner flame was extinguished during operation, potentially caused by fluctuations in gas pressure, a faulty flame rod, or venting issues.

Fixes:

• Inspect the Flame Rod: Clean or replace the flame rod if it’s dirty or corroded.

• Check Gas Pressure: Ensure that there are no fluctuations in the gas supply that could affect combustion.

• Examine Venting: Look for blockages, moisture, or debris in the vent pipes that could interfere with air intake and exhaust.

  
  

HVAC Insight:

Flame loss can impact not only the water heater but also connected HVAC systems that rely on the consistent thermal output of the water heater.

Electrical or Wiring Problems

Electrical issues such as power surges, loose connections, or damage to the internal PCB (printed circuit board) can prevent the system from functioning correctly.

Fixes:

• Check the Power Supply: Verify that the unit is plugged into a working outlet and that circuit breakers or GFCIs are not tripped.

• Inspect Wiring: If you're qualified, open the control panel and check for loose, burnt, or disconnected wires.

• Replace Fuses or Control Boards: If necessary, replace any blown fuses or consult an HVAC technician to test and possibly replace the control board.

  
  

Incorrect Temperature Settings or Thermostat Issues

Incorrect temperature settings or malfunctioning thermostats can cause the unit to fail to heat water to the desired temperature.

Fixes:

• Check Temperature Settings: Use the control panel to confirm that the temperature is set between 120°F and 140°F for optimal performance.

• Inspect External Thermostats: Ensure that external thermostats or mixing valves are not overriding the desired temperature settings.

• Examine Mixing Valves: Make sure that the mixing valve isn’t stuck in the cold position, as this can cause the water to remain cold.

  
  

Software Glitches or Control Board Malfunction

Software bugs or a malfunctioning control board can prevent the water heater from functioning properly, even if all other components are in good condition.

Fixes:

• Perform a Soft Reset: Reset the system through the control panel to resolve minor software glitches.

• Hard Reset: If problems persist, consult the user manual to perform a hard reset or factory reset.

• Replace the Control Board: If the issue continues, the control board may need to be replaced with a genuine Navien part.

  
  

Abnormal Air Pressure

An abnormal air pressure error is often related to venting issues, fan malfunctions, or faulty air pressure sensors that prevent proper combustion.

Fixes:

• Clean the Venting: Inspect both the intake and exhaust venting for blockages or damage.

• Inspect Air Pressure Sensor: Check the air pressure sensor tubing for clogs or wear.

• Replace Faulty Components: If necessary, replace the fan motor or air pressure sensor to restore proper function.

  
  

By addressing common issues and performing regular maintenance, you can keep your Navien tankless water heater running smoothly. Timely replacement of damaged Navien parts ensures optimal performance and a reliable hot water supply. If problems persist, it's best to consult a licensed HVAC professional for a safe and efficient repair.

Written by Allen Rode for PartsHnC, your trusted source for high-quality HVAC parts, including water heater components, air conditioner parts, and heat pump solutions.