Rinnai Error Code LOC: Controller locked (KCM) (Tankless)

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

Rinnai error code LOC on a tankless water heater means: Controller locked (KCM). It is also called Rinnai diagnostic code LOC.

Low severityTankless Water HeaterKCM (RUCS/RUS)

Homeowner? What Rinnai code LOC means for you

Usually minor Your tankless water heater is reporting: Controller locked (KCM). 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 LOC mean?

On the MC-601-US controller of KCM units, a locked controller cycles the display through LOC, the temperature setting, and any active diagnostic code. Locking one controller locks every controller in the system.

Applies to: Rinnai KCM tankless with MC-601-US controller

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.

Other Rinnai Tankless codes

Code	Meaning
FL	Forced low-fire combustion
In	Initial setting: indoor installation
In Use fast flash	In Use light rapid flash
In Use slow flash	In Use light slow flash
In Use solid	In Use light steady
LC	Scale build-up in heat exchanger (LC, LC0–LC9, 00)
Lock key	Controller locked (key symbol)
LPG	Initial setting: propane (LPG)
Maint monitor	KCM maintenance monitor (flow and outlet temperature)
Mute	Controller key beeps on/off
nG	Initial setting: natural gas
ON	Hot water running (controller installed)

All Rinnai Tankless Water Heater error codes →

Rinnai code LOC: homeowner questions

What does Rinnai code LOC mean?

Controller locked (KCM). On the MC-601-US controller of KCM units, a locked controller cycles the display through LOC, the temperature setting, and any active diagnostic code. Locking one controller locks every controller in the system.

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

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

Can I reset Rinnai code LOC myself?

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

Who can fix Rinnai code LOC 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 KCM Series Manual (U328-0700X04), p.55. 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.