Rinnai Error Code In Use solid: In Use light steady (Tankless)

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

Rinnai error code In Use solid on a tankless water heater means: In Use light steady. It is also called Rinnai diagnostic code In Use solid.

Low severityTankless Water HeaterSENSEI RX/CX · SENSEI

Homeowner? What Rinnai code In Use solid means for you

Usually minor Your tankless water heater is reporting: In Use light steady. 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 In Use solid mean?

The In Use light on the integrated controller stays on steadily while the burner is lit and hot water is flowing. Normal operation. On units with an external pump this is one of three In Use patterns.

Applies to: Rinnai SENSEI tankless (RU, RUR, RSC, CU) and SENSEI RX/CX (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 In Use solid

Show all 30 models

CU160e CU160i CU199e CU199i CX160i CX199i CXP160i CXP199i RSC160e RSC160i RSC199e RSC199i RU130e RU130i RU160e RU160i RU180e RU180i RU199e RU199i RUR160e RUR160i RUR199e RUR199i RX130i RX160i RX180i RX199i RXP160i RXP199i

Other Rinnai Tankless codes

Code	Meaning
FF	Maintenance performed (history marker)
FH	Forced high-fire combustion
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
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)
Maint monitor	KCM maintenance monitor (flow and outlet temperature)
Mute	Controller key beeps on/off

All Rinnai Tankless Water Heater error codes →

Rinnai code In Use solid: homeowner questions

What does Rinnai code In Use solid mean?

In Use light steady. The In Use light on the integrated controller stays on steadily while the burner is lit and hot water is flowing. Normal operation. On units with an external pump this is one of three In Use patterns.

Is it safe to keep using my tankless water heater with code In Use solid?

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

Can I reset Rinnai code In Use solid myself?

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

Who can fix Rinnai code In Use solid 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

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Source: Rinnai N-Series Residential (100000467) / with Pump (100000508) / Commercial (100000504) / RSC SENSEI (100000773) Installation and Operation Manuals, 5.3.3 In Use Light p.70; Rinnai SENSEI RX Residential Installation and Operation Manual (100000839), 5.3 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.