Navien Tankless Water Heater Not Turning On: Fix It Now

Navien Tankless Water Heater Not Turning On: Fix It Now

In today’s energy-conscious homes, tankless water heaters play a vital role in efficient HVAC system performance. Navien leads the market with its innovative technology and eco-friendly designs. Still, issues can arise, especially when the system suddenly won’t turn on. In many cases, the root of the problem is tied to faulty or neglected Navien tankless water heater parts. Whether you're a homeowner or an HVAC professional, understanding how to pinpoint and resolve these component-level issues is key to restoring your system’s functionality quickly and effectively.

Common Causes and Fixes for Navien Tankless Water Heater Not Turning On

Here are the common causes and effective fixes for a Navien tankless water heater not turning on.

Power Supply Issues

One of the first things to check when your Navien tankless water heater isn’t turning on is the power supply. If the unit is not receiving power, the system simply won’t activate. Common reasons include a tripped circuit breaker, a malfunctioning outlet, or faulty internal wiring.

Fixes:

• Check the Circuit Breaker: A tripped circuit breaker is often the culprit. Go to the electrical panel, check if the breaker associated with the water heater has been tripped, and reset it if necessary. This simple fix can solve the problem in many cases.

• Test the Outlet: The outlet the water heater is plugged into may not be working. To check, plug in a different device, such as a lamp or phone charger. If that device doesn’t work either, the outlet may need repair or replacement.

• Inspect the Fuse: In some cases, the fuse on the unit’s printed circuit board (PCB) might be blown. Turn off the power, open the access panel of the heater, and inspect the fuse. If it's blown, replace it with one of the same rating.

• Examine Wiring Connections: Loose or corroded wires can also prevent power from reaching the unit. Check the connections inside the unit to ensure everything is tight and secure.

  
  

Ignition System Failure

If your Navien tankless water heater turns on but doesn’t ignite, the ignition system could be the issue. Problems could arise with the igniter, flame rod, or faulty wiring that prevents the system from detecting a flame.

Fixes:

• Clean the Flame Sensor: The flame sensor detects whether the burner has ignited. Over time, carbon buildup can cause the sensor to malfunction. Clean it with fine sandpaper to remove any debris or carbon and restore its function.

• Inspect the Igniter: The igniter may have cracked or worn out. If the igniter isn’t working properly, it will need to be replaced.

• Check Wiring Connections: If the ignition wiring is loose or corroded, the heater may not ignite. Inspect the ignition-related wiring to ensure it’s properly connected and free from wear or corrosion.

• Replace Faulty Components: If cleaning the flame sensor or inspecting the wiring doesn’t help, you may need to replace the ignition transformer or relay. These components are critical to the ignition process.

  
  

Gas Supply Problems

A lack of gas supply or low gas pressure can prevent the unit from igniting and functioning properly. Without the right amount of fuel, the heater won’t be able to create heat.

Fixes:

• Ensure the Gas Valve is Open: Check that the gas valve to the unit is fully open. If it's not, simply open it to restore the flow of gas.

• Test the Gas Pressure: Low gas pressure can prevent the heater from functioning. Use a manometer to check the gas pressure and ensure it is within the manufacturer’s recommended range. If it’s too low, contact your gas supplier for assistance.

• Check for Leaks: Gas leaks are a serious safety concern. Apply soapy water to the gas lines and look for bubbles. If any leaks are detected, repair them immediately.

• Examine the Gas Lines: Ensure the gas lines are properly sized and free of blockages. If you’ve recently switched to a different type of gas (e.g., natural gas to propane), verify that the conversion was performed correctly.

  
  

Low or No Water Flow

Navien tankless water heaters require a minimum flow rate to activate. If the water flow is too low, the system will not turn on. This could be due to partially closed valves, a clogged inlet filter, or a malfunctioning flow sensor.

Fixes:

• Verify Valve Positions: Check both the cold and hot water inlet valves to make sure they’re fully open. A partially closed valve could restrict the water flow enough to prevent the heater from turning on.

• Clean the Inlet Filter: Over time, sediment and debris can clog the inlet filter, which reduces water flow. Clean the filter by removing it and rinsing it under water. If it’s too clogged, replace it.

• Inspect the Flow Sensor: The flow sensor measures the rate at which water flows into the heater. If it's malfunctioning, the unit may fail to detect the flow and won’t start. Remove and clean the sensor if necessary.

• Check Water Pressure: If the overall water pressure is low throughout your home, it could prevent the tankless water heater from activating. Installing a water booster pump may be necessary to increase the pressure.

  
  

Frozen Pipes or Components

In colder weather, water lines or internal components of the tankless water heater can freeze, blocking the flow of water and causing the system to shut down.

Fixes:

• Thaw the Pipes: If you suspect frozen pipes, turn off the water supply to the unit and carefully thaw the pipes using a hairdryer or space heater. Never use an open flame, as this could cause damage.

• Activate Freeze Protection: Many Navien models have built-in freeze protection. However, it requires power to activate. Ensure that the heater is plugged in and powered on during cold weather.

• Insulate Pipes: To prevent future freezing, insulate exposed water pipes or use heat tape on vulnerable sections. This will help maintain water flow even in low temperatures.

  
  

Ventilation Blockages

Navien tankless water heaters rely on proper venting to operate safely. Blocked vents can cause the unit to go into a safety shutdown mode.

Fixes:

• Clear the Vent Terminals: Inspect the vent terminals outside the house for any blockages, such as snow, leaves, or debris. Remove any obstructions to restore proper ventilation.

• Inspect the Venting System: If the venting system is too long or improperly installed, it can disrupt airflow. Check that the vent pipes are installed correctly according to the manufacturer’s guidelines.

• Check the Air Intake Filter: Some models have an air intake filter that should be cleaned regularly. A clogged air filter can reduce airflow, causing the unit to malfunction. Clean or replace the filter as needed.

  
  

Overheating or High-Temperature Lockout

Tankless water heaters can overheat if there’s mineral buildup, poor water flow, or a blockage in the venting system. If the unit detects excessive heat, it will shut down to protect itself.

Fixes:

• Flush the Heat Exchanger: Mineral buildup, such as limescale, can accumulate inside the heat exchanger. Use a descaling solution to flush the system and remove these deposits.

• Check the Inlet Filter: A clogged inlet filter can reduce water flow, causing the system to overheat. Regularly clean or replace the filter to maintain proper flow.

• Inspect the Exhaust Venting: Ensure that the exhaust vent is not obstructed and is capable of venting hot gases efficiently. Improper venting can cause the unit to overheat.

• Replace Temperature Sensors: If the temperature sensors are malfunctioning, they may trigger an overheating lockout even when the temperature is normal. In this case, replacing the faulty sensors is necessary.

  
  

Faulty Sensors

Sensors monitor various functions of the water heater, such as water flow, temperature, and ignition. If a sensor malfunctions, it may prevent the heater from turning on.

Fixes:

• Test Sensor Readings: Many Navien models feature a diagnostic mode that allows you to test the sensor values. If any of the sensors show incorrect readings, they may need to be replaced.

• Check Wiring Connections: Inspect the wiring for the sensors to ensure that there are no loose connections or damaged wires. Reconnect or replace as necessary.

• Replace Malfunctioning Sensors: If a sensor is beyond repair, replacing it with an OEM part will restore the unit’s functionality.

  
  

Blocked Condensate Drain

Navien tankless water heaters are designed to produce condensate as a byproduct of the combustion process. A blocked condensate drain can prevent the unit from operating.

Fixes:

• Flush the Condensate Line: Remove the condensate line and flush it with warm water to clear any blockages that may have accumulated over time.

• Clean the Condensate Trap: Regularly clean the condensate trap to prevent buildup of debris, which could block the drainage.

• Insulate the Drain Line: In cold weather, the condensate line may freeze. Insulate the drain line to prevent it from freezing, which could block the drainage.

  
  

Control Board Failure

The control board is the “brain” of your tankless water heater, managing all of the unit’s operations. Over time, it can wear out or become damaged, causing the heater to stop working.

Fixes:

• Inspect the Control Board: If your unit is unresponsive, visually inspect the control board for signs of damage, such as burnt areas or loose connections.

• Reset the System: Sometimes, resetting the control board by disconnecting the power for a few minutes can resolve minor electronic glitches.

• Replace the Control Board: If the control board is irreparably damaged, it will need to be replaced. Ensure you install a compatible replacement to restore functionality.

  
  

While a Navien tankless water heater not turning on can stem from various causes, most issues can be resolved with systematic troubleshooting and routine maintenance. Regular inspection and replacement of worn Navien tankless water heater parts can prevent many of these problems before they occur. If basic fixes don’t restore your unit’s function, it’s best to consult an HVAC professional to ensure safe and accurate repairs.

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.