What causes Rinnai Tankless Water Heater 15?

A temporary control glitch that clears after a full power reset (Rinnai's first step and the way its tech sheet says to clear the code). Loose, damaged or broken connections on the gas valve or solenoid wiring harnesses. On SENSEI RX/CX models, the black reed switch on the back of the gas valve not seated in its proper position (per the newer manual revision). A venturi control device whose voltage or coil resistance at the PC board is out of Rinnai's range. A fan motor that isn't operating properly. Restricted airflow through the intake or exhaust ports of the vent system. A failed gas valve assembly (which carries the venturi control) or a failed fan motor.

How do I fix Rinnai Tankless Water Heater 15?

Do a full power reset: switch off the heater's power at the breaker or unplug it, wait about a minute, and restore power. Rinnai's tech sheet says resetting the main power supply clears code 15. Go outside and make sure the vent termination and air intake aren't blocked by snow, ice, leaves or a nest, without taking the vent apart. Rinnai lists intake and exhaust airflow among the code 15 checks. On a condensing SENSEI model, check that the condensate drain line isn't kinked, clogged or frozen. That's a code 17 and code 10 check rather than code 15, but it's free and rules out a related airflow problem. Write down the code and any other codes that showed up before it. Your installer or Rinnai support will ask for the history. If 15 comes back after a reset, stop resetting and call a licensed professional or Rinnai support. Every remaining step is inside the gas valve and control wiring, and Rinnai's manual warns that you must be qualified to service gas systems. If you smell gas at any point, leave the house and call your gas company from outside.

When should I call a pro for Rinnai Tankless Water Heater 15?

Code 15 returns after a full power reset. Inspecting the gas valve and solenoid wiring harnesses for loose, damaged or broken connections, and on SENSEI RX/CX models confirming the reed switch on the back of the gas valve is seated correctly. Measuring the venturi control device at the PC board against Rinnai's Electric Circuit Table in the model's tech sheet and wiring diagram. For SENSEI models Rinnai's manual uses connector D, with 12 to 14 VDC on the supply pins and 35 to 41 ohms across each coil pair; RX/CX models use connector CN10 with different values. Checking that the fan motor runs properly and that airflow through the intake and exhaust vent isn't restricted. Replacing the gas valve assembly, then the fan motor, if the readings point there. If the heater is under warranty, contact Rinnai or a Rinnai-authorized professional instead of opening it yourself.

Code: 15🚿 Rinnai Tankless Water Heater

Rinnai Tankless Error Code 15: Venturi Control Fault on SENSEI Models (Meaning, Causes, Fixes)

Q: What does Rinnai Tankless Water Heater 15 mean?

Code 15 on a Rinnai tankless water heater means Venturi Control: the control board isn't getting the response it expects from the venturi control device on the gas valve, which sets the gas and air mix. Rinnai lists code 15 for its condensing SENSEI series. The one homeowner step is a full power reset; if the code comes back, the fix is wiring checks, readings at the control board, and usually a new gas valve assembly or fan motor, which is work for a licensed professional. Rinnai's Troubleshooting Tankless Water Heater Diagnostic Codes manual titles code 15 Venturi Control and lists it for SENSEI series heaters only; a newer revision of the same manual adds the SENSEI RX/CX series. The SENSEI Technical Sheet gives the same name and three remedies: make sure the venturi motor is operating correctly, replace the gas valve assembly, and clear the code by resetting the main power supply to the water heater. The venturi control device is part of the gas valve assembly, and the board checks it electrically. Rinnai's troubleshooting steps start with a power reset, then the gas valve and solenoid wiring harnesses, then voltage and resistance readings of the venturi control device at the PC board, then the fan motor and the airflow through the intake and exhaust vent, and finally replacing the gas valve assembly or the fan motor. Code 15 is a different fault from code 17 (Venturi Blockage), which is about debris inside the venturi.

Reviewed 2026-10-23 · Based on 3 manufacturer & service sources

What the code means

Rinnai's Troubleshooting Tankless Water Heater Diagnostic Codes manual titles code 15 Venturi Control and lists it for SENSEI series heaters only; a newer revision of the same manual adds the SENSEI RX/CX series. The SENSEI Technical Sheet gives the same name and three remedies: make sure the venturi motor is operating correctly, replace the gas valve assembly, and clear the code by resetting the main power supply to the water heater. The venturi control device is part of the gas valve assembly, and the board checks it electrically. Rinnai's troubleshooting steps start with a power reset, then the gas valve and solenoid wiring harnesses, then voltage and resistance readings of the venturi control device at the PC board, then the fan motor and the airflow through the intake and exhaust vent, and finally replacing the gas valve assembly or the fan motor. Code 15 is a different fault from code 17 (Venturi Blockage), which is about debris inside the venturi.

Likely causes

A temporary control glitch that clears after a full power reset (Rinnai's first step and the way its tech sheet says to clear the code)
Loose, damaged or broken connections on the gas valve or solenoid wiring harnesses
On SENSEI RX/CX models, the black reed switch on the back of the gas valve not seated in its proper position (per the newer manual revision)
A venturi control device whose voltage or coil resistance at the PC board is out of Rinnai's range
A fan motor that isn't operating properly
Restricted airflow through the intake or exhaust ports of the vent system
A failed gas valve assembly (which carries the venturi control) or a failed fan motor

Safe DIY checks

⚠ Before you start

Unplug the appliance (or switch off its breaker) and shut off the water supply valves before removing panels or disconnecting hoses. Keep towels handy for residual water.

Do a full power reset: switch off the heater's power at the breaker or unplug it, wait about a minute, and restore power. Rinnai's tech sheet says resetting the main power supply clears code 15.
Go outside and make sure the vent termination and air intake aren't blocked by snow, ice, leaves or a nest, without taking the vent apart. Rinnai lists intake and exhaust airflow among the code 15 checks.
On a condensing SENSEI model, check that the condensate drain line isn't kinked, clogged or frozen. That's a code 17 and code 10 check rather than code 15, but it's free and rules out a related airflow problem.
Write down the code and any other codes that showed up before it. Your installer or Rinnai support will ask for the history.
If 15 comes back after a reset, stop resetting and call a licensed professional or Rinnai support. Every remaining step is inside the gas valve and control wiring, and Rinnai's manual warns that you must be qualified to service gas systems. If you smell gas at any point, leave the house and call your gas company from outside.

🛠 When to call a pro

Code 15 returns after a full power reset.
Inspecting the gas valve and solenoid wiring harnesses for loose, damaged or broken connections, and on SENSEI RX/CX models confirming the reed switch on the back of the gas valve is seated correctly.
Measuring the venturi control device at the PC board against Rinnai's Electric Circuit Table in the model's tech sheet and wiring diagram. For SENSEI models Rinnai's manual uses connector D, with 12 to 14 VDC on the supply pins and 35 to 41 ohms across each coil pair; RX/CX models use connector CN10 with different values.
Checking that the fan motor runs properly and that airflow through the intake and exhaust vent isn't restricted.
Replacing the gas valve assembly, then the fan motor, if the readings point there. If the heater is under warranty, contact Rinnai or a Rinnai-authorized professional instead of opening it yourself.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Combustible gas leak detector

For peace of mind around a gas water heater. A real gas smell means leave and call the gas company, not a DIY check.

[affiliate link slot: AFFILIATE_SLOT_GAS_LEAK_DETECTOR]

⚙

Digital multimeter

What a technician uses for Rinnai's voltage and resistance checks at the control board. Only for qualified gas-appliance service.

[affiliate link slot: AFFILIATE_SLOT_MULTIMETER]

⚙

Rinnai gas valve assembly or fan motor (exact part for your model)

Technician part only. Rinnai's last steps for code 15 are replacing the gas valve assembly, then the fan motor.

[affiliate link slot: AFFILIATE_SLOT_BLOWER_MOTOR]

Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.

Rinnai Tankless Error Code 15: Venturi Control Fault on SENSEI Models (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Combustible gas leak detector

Digital multimeter

Rinnai gas valve assembly or fan motor (exact part for your model)

Related codes

Sources