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Rinnai Tankless Error Codes: How to Troubleshoot

Red dice spelling ERROR

When your Rinnai tankless water heater has a problem, an error code is shown on the display panel. Frequently, there's a few steps you can take to troubleshoot the issue, you may even be able to get your tankless back up and running. But at bare minimum, you'll have an idea of the problem before you call for repairs.

Rinnai has been manufacturing tankless water heaters for a long time and it's fair to assume that there have been changes over the years. This makes your owners manual your best resource for troubleshooting your unit. It'll have the information you need for your specific model.

Error Codes for Rinnai Tankless Water Heaters


A word of warning: We recommend contacting a professional to do the repairs for you. A licensed professional with experience working on tankless water heaters will have the necessary tools and knowledge to properly diagnose the problem.

If your unit is under warranty, doing the work yourself, or disassembling your unit could void your warranty. 

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Error Code 02

No Burner Operation During Freeze Protection Mode

If your tankless is displaying and error code 02, you'll need to call a professional.

Error Code 03

Power Interruption During Bath Fill

If there was a power outage or interruption its possible that once the power is restored the water won't flow. When this happens, try the following:

  • Shut off all the hot water fixtures in your house.
  • On the temperature controller, press the on/off button twice.
  • If the error code displays again, you'll need to call a professional.

Error Code 05

Bypass Servo

If you have bypass valves installed on your tankless water heater, you may see an error code 05.

  • Turn the power to the tankless off. 
  • Turn the power to the tankless back on, and fire the tankless up.
  • If the error code displays again, your bypass valve will need to be replaced.

Error Code 10

Air Supply or Exhaust Blockage

If you see an error code 10, check the following:

  • Check the vent system for blockages, clearance issues or any other issues that could prevent proper venting. Don't forget to check the vent outside.
  • Contact a professional if you are unable to find an issue with your vent. There are additional diagnostic tests that can be run.

Error Code 11

No Ignition

Caution: It's best to contact a professional to investigate an error code 11. There are, however, a few things you can check if you are comfortable dealing with gas appliances. 

  • Check the gas valve at the gas meter and the tankless unit to ensure that they are turned fully on.
  • Check that the igniter is functioning properly.
  • If the igniter is properly working and the tankless is being supplied with gas, then you need to call a professional.
Blue gas flame in a water heater

Error Code 12

IMPORTANT: There are two types of error code 12. The following will help you determine which code 12 is your problem:

  • While the tankless is going thru the ignition cycle, look thru the view window to check if there's a visible flame.
  • If you were able to see a flame in the burner box, either during operation and/or during the ignition cycle, you have a flame failure (gas) error code 12. This is the most common.
  • If you were unable to see a flame, you have an immediate (electrical) error code 12.
  • Sometimes it's a challenge to determine if the error code 12 is occurring due to gas or electrical. If so, turn off the gas and try to fire the unit on. If it displays a code 11 the problem is gas - If the code 12 displays, it's an electrical short.
Flame Failure (Gas)

If the error code 12 is due to flame failure, you should call a qualified professional. Never attempt to solve this problem yourself.

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Immediate (Electrical)

Depending on which Rinnai tankless model you own, you may see an error code 19 instead. Regardless, the code will display when the water supply is first turned on.

  • This error code is an indicator that there's a short circuit within the tankless. The problem could be in a wiring harness, bypass valve, water flow control or another component within the DC circuit.
  • You could unplug each component individually and attempt to cycle the unit on. If the tankless cycles 3-times after unplugging a component, you'll know the problem is from the unplugged component.
  • However, for the average user, your best choice is to contact a professional to do the troubleshooting for you.

Error Code 14

Thermal Fuse or Overheat

Important: This error code should be taken very seriously. An error code 14 indicates that your Rinnai is over heating. The issue could either be the bi-metal safety switch or the thermal fuses.

Remove the cover and look for discoloration on the surface of the heat exchanger in the area where the combustion box meets the copper section. Check the internal components in and around this area.

Bi-Meta​​​​l Switches
  • The thermo-fuses are wrapped around the heat exchanger with the bi-metal safety switch mounted to either the top left front or the top right of the heat exchanger.
  • In most situations, the bi-metal switch will simply reset itself after the unit cools. Once the switch resets, the tankless will be able to operate again. 
  • However, if the root problem is not corrected, the bi-metal switch will continue to trip. This is because the same problem will cause the heat exchanger to reach it's hi-limit temperature range. 
Thermo-fuses
  • The thermo-fuses are wrapped around the heat exchanger. When they blow, they will need to be replaced. There is no way to reset these fuses.
  • If your thermo-fuses blow, it's generally best to call a professional to replace them. The heat exchanger will need to be removed, and the tankless should have a detailed inspection.

Error Code 16

Over Temperature Warning

An error code 16 means that the tankless shutdown to protect itself from damage. It's sensors recorded the room temperature to be above 104 degrees Fahrenheit for more than 10 minutes. 

Warning: Although there are a few things that you can check before calling for service, only a professional should do any repairs to the electrical or gas system.

  • Check that the air filter is clean and in good repair. Specifically look for clogging.
  • Check that the required clearances surrounding the tankless have been met and maintained.
  • Check outside where the vent terminates. There should be no obstructions.

Error Code 19

Electrical Grounding

An error code 19 indicates that there's an electrical short in one of your components. In most cases, it's best to call a professional to troubleshoot this issue.

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Error Code 25

Condensate Trap is Full

There's a number of issues that could be causing an error code 25. 

  • Check that the condensate drain line is not blocked.
  • Open the cabinet and check that the condensate tank and trap are not blocked. 
  • Check that the air gap between the condensate drain line and the unit has been maintained. 
  • Inspect the sensor wiring harness. Look for loose, damaged or broken connections between the PC board and the sensor.
  • Replace the sensor if the tank is properly draining, but you are still seeing an error code 25. 

Error Code 31

Burner Thermocouple

If your Rinnai tankless throws and error code 31, you should contact a professional to inspect your unit's gas system.

Error Code 32

Outgoing Water Temperature Thermistor Fault

An error code 32 often means that the sensor is faulty and needs to be replaced. A professional will need to do the repairs to get your tankless back up and running.

Error Code 33

Heat Exchanger Outgoing Thermistor

In most cases, it's typically best to contact a professional to troubleshoot this error code. They'll have the training and tools to find and resolve the problem.

Although, if you are comfortable, you could drain down the tankless and remove and check for lime scale build-up on the thermistor.

Error Code 34

Combustion Air Temperature Thermistor

This error code will only display on indoor tankless models. If you see an error code 34, you should contact a professional to troubleshoot and make repairs.

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Error Code 41

Freeze Protection Sensor

This error code will only display on outdoor models. If the outside air temperature thermistor is disconnected or open, the tankless will display an error code 41 and alternate to the set point temperature.

In the above senerio, the unit will continue to operate. Once the root problem has been repaired, the error code will clear. A few other things to check are listed below: 

  • Note: When the freeze protection sensor/thermistor is shorted, damaged or unplugged, some models will allow the tankless to fire-up and will immediately flash an error code 41. While others will fire-up and then alternate between an error code 41 and the temperature set point. 
  • Inspect the sensor wiring harness. Look for broken, damaged or loose connections between the PC board and the sensor.
  • Check that the sensor is not covered with insulation and that it is open to the air outside. 
  • Contact a professional.

Error Code 51

Inlet Water Temperature Sensor

The Rinnai Tankless will display an error code 51 if the the inlet water temperature thermistor is disconnected or open. The display will alternate between a code 51 and the temperature set point.

If you have a code 51 issue, the unit will continue to operate. However, the code will continue to display until the underlying cause has been resolved.

Contact a professional to troubleshoot and repair the problem.

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Error Code 52

Modulating Solenoid Valve Abnormal

Contact a professional to troubleshoot and repair an error code 52.

Error Code 57

Burner Overheat Bi-Metal Switch

There are two bi-metals located on the rear of the burner assembly. If one of these two opens, your unit will display an error code 57. The tankless may or may not be operating when this code is displaying.

The code will continue to display until the problem is repaired. Once repaired, a hard reset (turn the power off to the unit and then back on) will need to be performed for the code to stop displaying. 

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Error Code 58

Secondary Heat Exchanger Sensor

An error code 58 displays if the secondary heat exchanger has one of the two bi-metals open. The tankless may or may not be operating when the code is showing. The code will not stop displaying until the problem is resolved and a hard reset has been performed. 

  • Although, the problem could be related to the wiring between the sensor and the PC board, there is a chance that you can fix this problem yourself. 
  • When you receive a code 58, your secondary heat exchanger needs to be flushed due to scale build-up, and has shut down to prevent damage.
  • If you live in an area with hard water, you should use a water softner to help protect your tankless water heater.
  • Flush your tankless by following the directions in your manual, or read our article to learn how.
  • After flushing, perform a hard reset by turning the power off and back on to the unit. If the error code does not disappear, you should call for service.

Error Code 61

Combustion Fan Motor

This error code should be resolved by a professional as they will need to measure the winding resistance of the fan motor. However, there are a few things that you can check. 

  • Important: Shut off the power to the tankless water heater before proceeding.
  • The problem could be electrical. Check the wiring harness between the PC board and the fan motor. Look for loose, broken or damaged connections.
  • With the power off, remove the fan motor. Check that the blower wheel is turning freely.
  • Inspect the fan housing. Look for debris or other obstructions that could prevent the fan wheel from turning.
  • If the fan wheel is spinning freely and there are no obstructions, you should call a professional to troubleshoot and repair your tankless.

Error Code 63

Circulation Flow Rate Dropped Below 1.3 GPM

If your Rinnai throws an error code 63, many people simply choose to call for service instead of troubleshooting the issue themselves. However, there are a few things you can check if you are a DIY kind of person. 

  • Check if the tankless is producing a water flow using the temperature controller by pressing the "UP" button for 3 seconds and then the "ON/OFF" button. The number displayed will be your flow rate. (ie. 7 = 0.7 gpm, 25 = 2.5 gpm).
  • If the flow rate was below 1.3 gpm, bleed the air from the pump and system tank. 
  • Remove and clean the inlet water filter.
  • Check that the water supply to the tankless is at a flow rater of 6 gpm or higher.
  • Check that the inlet water pressure to the tankless is between 30 to 50 psi.
Water flowing into a glass

Error Code 65

Water Flow Servo

Before calling for repair, check to see if the code resets when you perform a hard reset, by shutting the power off to the water heater and then turn it back on. 

If the code reappears, the water flow servo valve did not close during the bath fill function. Shut off the water flow and call a professional to troubleshoot the problem for you. 

Error Code 70

PC Board Fault

Contact a professional to troubleshoot and replace the PC Board.

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Error Code 71

Solenoid Valve Fault

An error code 71 means that one of your solenoid valves has failed. There are 4 solenoid valves (SV0, SV1, SV2 and SV3), and a number of different issues that could be causing this error code.

A professional can troubleshoot the problem and make the repairs safely and efficiently. 

Error Code 72

Flame Sensing Device Fault

Although we recommend having a professional work on this problem for you, there are a few things you can check yourself.

  • Warning: Shut off the gas, water, and electrical supply to the tankless water heater before proceeding.
  • Inspect the wiring harnesses from the flame rods to the PC board. Look for broken, damaged or loose connections.
  • Check that the flame rod is touching flame when the unit fires.
  • Remove the flame rod. Look for carbon build-up. Clean if needed.
  • Inspect the inside burner. Look for debris build-up which could cause the flame rod to short out.
  • Check that the flame rod is maintaining at least a 1 micro amp output.

Error Code 73

Burner Thermocouple Fault

When your unit displays an error code 73, you should call a professional for repair. They may need to replace the burner thermocouple and possibly even the PC board.

Error Code 79

Water Leakage Detected

If you're comfortable doing some troubleshooting, you may be able to determine the problem yourself. If the issue is the heat exchanger and/or the internal piping, you'll most likely need to call a professional. However, if the issue is the sensor, you may be able to fix it yourself.

  • Inspect the wiring harness on the leak detector. There may be damaged or loose wires.
  • Inspect the heat exchanger and all the internal piping within the tankless. Look for leakage.
  • If you don't find any leakage, look inside the cabinet. Specifically check the bottom pan of the tankless for signs of pooling water. 
  • If you find evidence of water pooling, dry off the leak sensor as well as the inside of the cabinet. Restart the tankless.
  • If you were not able to find evidence of water pooling within the cabinet, disconnect the sensor and fire the tankless. 
  • If the tankless operates without the sensor in place, the sensor will need to be replaced.
Water faucet with a no sign

No Error Code

Water Flow is Activated, but Nothing Happens

If your water heater isn't working, but it doesn't throw an error code, there are a few things it could be. Check the following before calling for service:

  • Remove and clean the water inlet filter.
  • If you just installed your tankless, check that the hot and cold water lines are correctly attached. If the lines are reversed, the unit will not work.
  • Check that the minimum flow rate is reached. If you are not meeting the minimum flow rate the unit will not fire.  
  • Check that the water flow control turbines are not obstructed. They should spin freely.

Code LC, LC0 - LC9

Scale Build-up in Heat Exchanger

Your tankless should continue to work when it throws an error code LC, LC0 - LC9, although some newer units may shut down to prevent damage.

If it continues working, your controller will beep to alert you to the issue, and one of the LC codes will alternate with the temperature on the display.

You should flush your tankless as soon as possible to prevent damage to your heat exchanger. Check your owners manual for directions, or we have listed the procedure here

Code FF

Serviceman has Serviced Product

Either maintenance or repair has been conducted on your unit when a code FF is used.

After making repairs to your tankless, the technician will enter a code FF. This alerts the system that any codes that occur after the FF code was entered occurred upon completion of the repairs.

It's a bit like drawing a line to help keep track of the error codes. One example of its use is if the same error code occurs after the code FF was entered, the technician will know that the repairs made did not solve the problem.