If your Navien tankless water heater is providing no hot water at low flow situations, your flow sensor may need replacing. When there is a demand of hot water the flow sensor will send signals the burners to ignite and heat the water.
But if your water heater flow sensor become faulty or not working it does not send signals to the burner when low flow of water is detected and sometimes it does not send signal at all, which results in getting cold waters when low flow faucets are used and getting hot water only when high flow faucets are used, or sometimes we get cool water on all faucets. With easy simple steps our water heater expert Joseph will explain how to replace a flow sensor on your Navien tankless water heater with only simple and minimum tools. In this article we are considering replacing Flow sensor for Navien NPE A2 but its nearly same for other models also.
Tools Needed
- Phillips head screwdriver – for removing screws
- Pliers – to tighten and loosen service caps
- Small container – for collecting drained water
- Paper towel – for drying any residual moisture
- Replacement flow sensor – suitable for your specific Navien model
Steps to Replace the Flow Sensor
1. Turn Off Power and Water Supply
- Power Off: First before doing anything disconnecting the power to your water heater. Unplug it or turn off the circuit breaker to avoid electrical hazards when touching and working with the unit.
- Shut Off Water Valves: Next, locate the hot water outlet and cold water inlet valves on your water heater. Turn both valves off to stop water from flowing through the unit.
2. Drain the Water Heater
- Open Service Caps: Use your pliers to loosen and remove the service caps on both the hot and cold water valves. Doing this allows any remaining water in the heater to drain out.
- Collect Water: Place a container underneath the valves to catch any drained water. This prevents water from spilling and keeps the workspace dry.
3. Remove the Heater’s Front Access Cover
- Unscrew Cover Screws: Using your Phillips head screwdriver, remove the four screws holding the access cover on the front of the water heater.
- Remove the Cover: Lift and carefully pull away the cover. Navien units have a hooked lip that secures the cover even when the screws are removed, so gently lift it off without forcing.
4. Locate and Disconnect the Flow Sensor
- Identify the Cold Water Inlet Line: Inside the heater, locate the cold water inlet. Follow this line as it leads to a distribution manifold that bends into the heater’s core.
- Disconnect Cables: You’ll see a few cables connected to the sensor. Start by unplugging the three-wire harness attached to the flow sensor. Then, carefully disconnect the blue cable connected to the temperature sensor. Push the connectors gently to avoid damage.
5. Release the Spring Clip
- Remove Spring Clip: In few models like NPE-210A there’s a small stainless steel spring clip securing the sensor. To remove it, press from an elevated angle with hand and pop it off carefully. The spring clip may have a bit of tension, so take care not to lose it.
6. Unscrew and Remove the Old Flow Sensor
- Unscrew Sensor: Using a Phillips screwdriver, unscrew the four screws securing the flow sensor in place. Ensure you use the correct screwdriver size (Phillips #2) to avoid stripping the screws.
- Detach the Sensor: Gently wiggle and slide the sensor off the inlet pipe. Be cautious of the O-ring inside the sensor; you’ll need to reuse or replace it if it’s damaged.
7. Inspect the New Flow Sensor
- Compare the Sensors: Check that your new sensor is identical to the old one. The model should match to ensure compatibility, as Navien flow sensors vary in design (e.g., some are straight, while others have angled connections).
- Understand the Components: The flow sensor consists of two main parts: the sensor that detects water flow and the blue temperature probe that monitors incoming water temperature. Together, they control the heating activation.
8. Transfer or Replace the O-Ring
- Check the O-Ring: Inspect the O-ring from the old sensor, as this rubber ring seals the sensor to prevent leaks. If it’s in good condition, transfer it to the new sensor. If it’s damaged, replace it with a new O-ring for secure sealing.
- Position the O-Ring on the Heat Exchanger: Slide the O-ring onto the heat exchanger’s inlet pipe. Make sure it’s positioned correctly to avoid any leaks in Navien water heater near the sensor.
9. Install the New Flow Sensor
- Attach the Sensor: Carefully position the new sensor onto the inlet pipe. Align it with the gasket, ensuring it sits correctly.
- Secure with Screws: Using the Phillips screwdriver, reinstall the four screws to secure the sensor. To avoid cross-threading, press the screw lightly, rotate counterclockwise until you feel it engage with the thread, and then screw it in. Tighten in a staggered manner for even pressure.
10. Reconnect the Cold Water Pipe and Spring Clip
- Reconnect Cold Water Pipe: Push the cold water pipe back onto the bottom of the flow sensor.
- Secure Spring Clip: Reattach the spring clip to hold the pipe and sensor securely. Check that the clip fits snugly to prevent leaks.
11. Plug in Sensor Cables
- Reconnect Wires: Insert the three-wire harness and the blue temperature probe cable into their respective connectors. These are keyed, so they won’t fit incorrectly, making reconnection straightforward.
12. Check for Moisture and Leaks
- Dry the Area: Use a paper towel to dry any water that might have come into contact with the heater body or cables. Ensuring everything is dry will prevent electrical issues.
- Inspect for Leaks: With everything in place, look for any signs of moisture around the sensor or connectors. Tighten any components if you notice leaks.
13. Close Service Valves and Restore Water Supply
- Close Drain Valves: Turn off the hot and cold water drain service valves, then tighten the service caps with pliers. They should be finger-tight, not overtightened.
- Open Water Supply: Slowly open the cold water inlet valve, followed by the hot water outlet. This allows water back into the heater.
14. Purge Air from the System
- Run Hot Water Tap: Open a hot water tap in the home (such as a kitchen or bathroom sink) to let any air trapped in the system escape. This prevents sputtering and allows water to flow smoothly.
15. Restore Power and Test the Heater
- Power On: Plug the heater back in or turn on the circuit breaker to restore power to the heater.
- Test the Heater: Open a low-flow faucet (e.g., kitchen or bathroom sink) to check if the heater ignites as it should. If it does, your new flow sensor is functioning correctly, even at low flow rates.
Key Points and Maintenance Tips
- Match Parts Precisely: Ensure the replacement flow sensor matches your specific Navien model to avoid compatibility issues.
- O-Ring Importance: The O-ring must be in place to prevent leaks; without it, water leaks and flow into unintended parts of the heater.
Conclusion
With just a Phillips screwdriver and pliers, you can replace the flow sensor on your Navien tankless heater in under 10 minutes. This DIY approach is a great way to save on repair costs and get your hot water flowing smoothly again.
If you heater unit has different type of flow sensor than we specified above and if the above steps doesn’t work, please comment below your model number of unit and sensor, we will help you as soon as possible. Thanks
