Rinnai Tankless Water Heater Error Code 55: How to Fix It

Q: What does error code 55 mean on a Rinnai water heater?

Error code 55 means the inlet water sensor is disconnected. This sensor monitors water flow and temperature at the cold water inlet. The heater will not operate until the sensor is properly connected.

Q: Can I reset my Rinnai water heater to clear error 55?

A simple reset may work if the sensor is temporarily misread. Turn off the unit for 10 minutes, then turn it back on. If the error reappears, you'll need to inspect the sensor connection or replace it.

Q: Where is the inlet water sensor located on a Rinnai tankless water heater?

The inlet water sensor is typically located on the cold water inlet pipe near the bottom of the unit, behind the front panel. It is a small device with wires attached.

Q: How much does it cost to replace a Rinnai inlet water sensor?

The sensor part itself costs between $20 and $50, depending on your model. If you hire a professional, labor costs can range from $100 to $200.

Q: Is error code 55 serious?

It is a medium-severity error. The water heater will not heat water until the sensor is reconnected or replaced. However, it does not indicate a dangerous problem, and the fix is usually straightforward.

Abstract

Error code 55 on your Rinnai tankless water heater indicates that the inlet water sensor is disconnected or faulty. This sensor monitors water flow and temperature at the cold water inlet. The error typically occurs if the wiring connection is loose or the sensor itself has failed. Follow these steps to diagnose and resolve the issue.