Navien Tankless Water Heater Error Code 434: How to Fix It

Q: What does Navien error code 434 mean?

Error 434 means the inlet water flow sensor is detecting low water flow. This is often due to a clogged filter, partially shut valve, or a faulty flow sensor.

Q: Can I still use hot water with error 434?

No. The heater will shut down to prevent damage. You need to fix the flow issue before operation.

Q: How do I clean the inlet filter on my Navien water heater?

Turn off power and water, unscrew the filter housing on the cold water inlet, remove the mesh screen, rinse or soak it in vinegar, then reinstall.

Q: How much does it cost to replace a Navien flow sensor?

A replacement flow sensor costs around $30-60. Professional installation may add $100-200.

Q: Will error 434 reset itself after fixing the issue?

Yes. After resolving the low flow cause, turn the heater off and on. The error should clear.

Abstract

Error code 434 on your Navien tankless water heater indicates the inlet water flow sensor is detecting low flow. This can be caused by a clogged filter, partially closed valve, or a faulty flow sensor. Follow these steps to diagnose and resolve the issue safely.