Rinnai Error Code rnS: Descaling finished, rinse now (Tankless)

Updated October 15, 2026 · by Aurora Star Tech Inc.

Rinnai error code rnS on a tankless water heater means: Descaling finished, rinse now. It is also called Rinnai diagnostic code rnS.

Low severityTankless Water HeaterSENSEI RX/CX

Homeowner? What Rinnai code rnS means for you

Usually minor Your tankless water heater is reporting: Descaling finished, rinse now. This code is usually informational or minor. The safe checks below often clear it; call us if it keeps showing up.

Safe things you can check yourself

Check that gas reaches the house: other gas appliances work, or the propane tank is not empty.
Make sure the heater is plugged in and its breaker is on. In winter, keep the power on: it protects the unit from freezing.
Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
Check that the hot and cold water valves under the heater are fully open.
If you have a remote controller, turn it off and on once. If the code comes back, call a technician.

Call (647) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Rinnai error code rnS mean?

Shown on RX/CX units when the 60-minute vinegar flush is complete, with a beep. It tells you to stop the pump and rinse the vinegar out of the heater.

Applies to: Rinnai SENSEI RX/CX tankless (RX, RXP, CX, CXP)

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Rinnai models that use code rnS

CX160i CX199i CXP160i CXP199i RX130i RX160i RX180i RX199i RXP160i RXP199i

Other Rinnai Tankless codes

Code	Meaning
Out	Initial setting: outdoor installation
Parameter mode	Parameter settings menu
Parameter settings	Parameter (installer settings) mode
Perf data	Performance data viewer (live readings and counters)
Performance data	Performance data readout mode
Priority light	Priority light on (this controller is in charge)
S	Venturi reset sequence: step S (SENSEI)
SE	Cascade diagnostic display (error on secondary unit)
SEt	Initial settings not yet confirmed
SS	Service Soon alert (also listed as 55)
t	Venturi reset sequence: step t
°C/°F	Temperature scale switch (Celsius / Fahrenheit)

All Rinnai Tankless Water Heater error codes →

Rinnai code rnS: homeowner questions

What does Rinnai code rnS mean?

Descaling finished, rinse now. Shown on RX/CX units when the 60-minute vinegar flush is complete, with a beep. It tells you to stop the pump and rinse the vinegar out of the heater.

Is it safe to keep using my tankless water heater with code rnS?

Usually yes. Code rnS is normally minor, but if it keeps coming back have it checked.

Can I reset Rinnai code rnS myself?

You can try one reset (power off for 30 seconds, then on). If Rinnai code rnS comes back, the cause is still there and a licensed technician should check it.

Who can fix Rinnai code rnS near me?

Aurora Star Tech Inc. repairs Rinnai tankless water heaters in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.

Homeowner help: Tankless Water Heater No Hot Water: What to Check

Troubleshooting guides

No hot water All brands · Tankless Water Heater
Water temperature fluctuates All brands · Tankless Water Heater
Checking PC board fuses and thermistors Rinnai · Tankless Water Heater
Enter installer parameter mode (A button on the PC board) Rinnai · Tankless Water Heater
First power-up setup: gas type and indoor/outdoor (RX/CX) Rinnai · Tankless Water Heater
Lock or unlock the controller (key symbol) Rinnai · Tankless Water Heater
Lock or unlock the KCM controller (LOC) Rinnai · Tankless Water Heater
Performance data readout (items 01 to 24) Rinnai · Tankless Water Heater
Reset after cleaning the venturi or replacing the gas valve (codes 17 / 52) Rinnai · Tankless Water Heater
Reset the Service Soon (SS) reminder Rinnai · Tankless Water Heater
Show live flow and outlet temperature on the KCM controller Rinnai · Tankless Water Heater
Show the last 9 stored codes (diagnostic history) Rinnai · Tankless Water Heater
Start descaling (vinegar flush) mode on the PC board Rinnai · Tankless Water Heater
Switch the controller between Celsius and Fahrenheit Rinnai · Tankless Water Heater
Turn controller key beeps on or off Rinnai · Tankless Water Heater
Weak or missing flame signal (flame rod checks) Rinnai · Tankless Water Heater

Source: Rinnai SENSEI RX Residential Installation and Operation Manual (100000839), 6.3 Flushing the Heat Exchanger, Quick-Flush p.68. Written in our own words as a summary; always check the original manual.

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.