Rinnai Error Code Maint monitor: KCM maintenance monitor (flow and outlet temperature) (Tankless)

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

Rinnai error code Maint monitor on a tankless water heater means: KCM maintenance monitor (flow and outlet temperature). It is also called Rinnai diagnostic code Maint monitor.

Low severityTankless Water HeaterKCM (RUCS/RUS)

Homeowner? What Rinnai code Maint monitor means for you

Usually minor Your tankless water heater is reporting: KCM maintenance monitor (flow and outlet temperature). 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 Maint monitor mean?

Information mode on the MC-601-US controller of KCM units that shows two live readings. Nothing is wrong when you use it.

Applies to: Rinnai KCM tankless (RUCS65i/75i, RUS65e/75e)

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
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)
LOC	Controller locked (KCM)
Lock key	Controller locked (key symbol)
LPG	Initial setting: propane (LPG)
Mute	Controller key beeps on/off
nG	Initial setting: natural gas
ON	Hot water running (controller installed)
Out	Initial setting: outdoor installation
Parameter mode	Parameter settings menu
Parameter settings	Parameter (installer settings) mode

All Rinnai Tankless Water Heater error codes →

Rinnai code Maint monitor: homeowner questions

What does Rinnai code Maint monitor mean?

KCM maintenance monitor (flow and outlet temperature). Information mode on the MC-601-US controller of KCM units that shows two live readings. Nothing is wrong when you use it.

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

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

Can I reset Rinnai code Maint monitor myself?

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

Who can fix Rinnai code Maint monitor 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.56. 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.