Takagi Water Heater Error Codes

Takagi Water Heater Error Codes [Ultimate Guide]

This is a complete guide on Takagi Water Heater Error Codes. What I will break down in this article: 

  • What and why will the error codes on Takagi water heaters pop up? 
  • Will walk you through the troubleshooting steps to erase the error message
  • How to reset your Takagi Tankless Water Heater?

Without further ado, let’s dive in. 

Table of Contents

10 Common Takagi Tankless Water Heater Error Codes

This chapter will describe the reasons that cause the unit to pop up error codes and walk you through the steps to reset them.  

Error Code 031

The green LED on the computer board will flash 1 time and throw the error code 031 on the controller display if you fine tune the DIP switch settings incorrectly. 

In most cases, setting the DIP switch incorrectly for the gas type your water heater is operated by is responsible for the error code 031. 

How To Fix: 

To erase this error code from the display, what you need to do is- 

  • Turn the unit off.
  • Unscrew the nuts that hold the front cover in place and pull it out. 
  • Locate the DIP switches on the computer board. Specifically, you can find the DIP switches on the center of the PCB. 

Now, adjust the DIP switch settings according to the following screenshots: 

DipSwitch Settings
*DipSwitch Settings*
DipSwitch Settings Upper Bank
*DipSwitch Settings Upper Bank*
DipSwitch Settings Lower Bank
*DipSwitch Settings Lower Bank*

Alternatively, you can call a service technician to make the adjustment of the DIP switch settings correctly. 

Takagi Tankless Water Heater Error Code 101

‘Abnormal combustion’- this is what the error code 101 stands for. Your Takagi water heater will flash this error code due to the following reasons: 

  • Feeding the unit with improper type of gas
  • Set the altitude DIP switches incorrectly 
  • Blockage in the intake air or exhaust 
  • The distance between the intake air terminal and the exhaust terminal is not within specification when you installed the water heater as a direct-vent system. 
  • Burner gets dirty

How To Fix: 

I wrote a guide on Takagi Tankless Water Heater Error Code 101. In that article, I broke down everything you need to know to reset the fault code 101. So, I recommend you check the article to resolve the issue.  

Takagi Water Heater Error Code 111

Error code on Takagi Tankless Water Heater indicates there is a problem with the ignition. Ignition failure can happen if: 

  • Hi-limit switch is malfunctioning or gets tripped
  • Igniter wire comes loose or gets broken 
  • Dirty flame sensor
  • Defective igniter
  • Heat exchanger is leaking 

How To Fix: 

Luckily, I already covered a guide on Takagi Tankless Water Heater Code 111. From this article, you can learn every troubleshooting step to erase the diagnostic code 111 from the controller display. So, it’s worth reading that article. 

Takagi Tankless Water Heater Error Code 121

The error code 121 will appear on the controller display when the flames disappear while the unit is supposed to be in operation.  

Several reasons are responsible for the unit to throw the error message 121, including: 

  • A tripped hi-limit switch
  • Insufficient gas supply 
  • Gas supply pressure isn’t within the specifications
  • Clear plastic tube gets detached
  • Dirty flame sensor
  • The overheat cutoff switch gets compromised
  • Venting gets blocked 
  • Defective PC board

How To Fix: 

First off, verify the hi-limit switch is working properly. To examine that, turn off the unit. Remove the front cover and locate the white button. Then, press the white button in. If you hear a click, understand you reset the hi-limit switch correctly. 

The next step you need to follow is- turn on the unit and discover the reasons that trip the hi-limit switch. It will be better to call a certified technician for help. 

Secondly, ensure sufficient amount of gas is supplied to the unit and the gas line is free of blockage. Don’t forget to inspect the gas regulator. If it’s at fault, replace it. 

Thirdly, check the gas pressure and ensure it’s within specifications. The gas pressure of a functional water heater should be 4” WC to 10.5” WC if you have a gas operated unit. On the other hand, the inlet gas pressure should be in this range: 8” WC to 14” WC if the water heater is propane operated. 

Fourthly, inspect that the clear plastic tube between the proportional gas valve and the combustion chamber doesn’t come loose. If it gets disconnected, reattach it. 

Fifthly, ensure there is no carbon buildup on the flame sensor. If the flame comes on for 1-2 seconds but gets extinguished, I bet the flame sensor gets coated with carbon deposits. To clean the flame sensor, follow these steps: 

  • Disconnect the water heater from the electric outlet to turn the water heater off.
  • Unscrew the front cover and pull it out. 
  • Remove the rod assembly from the center of the unit.
  • Locate the flame sensor on the rod assembly. Then, use a 100-grit sandpaper to scrub the flame sensor gently to clean the carbon buildup. 
  • After cleaning the flame sensor, reassemble the unit by following the steps in reverse. 

Sixthly, measure the continuity of the Overheat Cutoff Fuse. In this case, just turn off the unit and remove the front cover. 

Then, locate the OHCF that wraps around the heat exchanger. Next, find the white clip at the end of the two blue braided wires coming from the OHCF. 

And then, unplug the connection. What you need to do is- attach the manometer at the end of the OHCF to check continuity. If there is no continuity, the OHCF is at fault. 

Next, examine the venting for blockage. If there is any restriction, release it from the venting for proper water heater operation. 

Finally, take a look at the PC board to see whether it’s working properly or not. If it’s at fault, replace it. I recommend you hire a certified plumber to make this replacement. 

Error Code 311

On Takagi Water Heater, the fault code 311 stands for outlet thermistor failure. The outlet thermistor has failed because of the following reasons: 

  • The resistance at outlet thermistor goes out of range
  • Dirty thermistor
  • The outlet thermistor gets defective

How To Fix: 

To resolve the error code 311, go along with the following troubleshooting steps: 

1. Check the wiring on the outlet thermistor. You can find the outlet thermistor at the right side on the heat exchanger. 

2. Now, get a multimeter and check the resistance value of the outlet thermistor. A functioning output thermistor should give a reading of 9K ohms. If the resistance goes out of range, you should either clean the outlet thermistor or replace it. 

3. To clean the outlet thermistor, complete these steps: 

  • Drain your water heater first. If you don’t know how to drain the unit on Takagi, check this article on Takagi Water Heater Maintenance
  • Remove the fastener that holds the outlet thermistor in place and pull out the sensor probe. Then, clean the sensor probe. 
  • Replace the sensor probe and reinstall the fastener to secure the outlet thermistor. 

4. Replace the outlet thermistor if cleaning it will bring no luck for you. 

Error Code 321

The Takagi water heater will pop up the error code 321 if the inlet thermistor is malfunctioning. 

Like the outlet thermistor, the inlet thermistor will also get defective if its wiring comes loose or gets broken. Turns out, a dirty sensor probe or defective inlet thermistor can cause the unit to display the error message 321. 

How To Fix:

Follow the steps I described below to fix the error code 321: 

1. Check the wire connection of the inlet thermistor and ensure it’s free of burns. You can find the inlet thermistor embedded in the water inlet connection. 

2. Measure the resistance value of the inlet thermistor. The resistance valve should be 9K ohms if the inlet thermistor is functional. 

3. Clean the inlet thermistor: 

  • Drain your Takagi water heater.
  • Remove the front cover and locate the PC board. Then, pull out the PC board to access the inlet thermistor. 
  • Pull out the sensor probe by removing the screw. 

4. If the error code still persists, you must replace the inlet thermistor with a new one.

Error Code 331

Unlike the error code 321, this error code (331) is also related to the thermistor issue. When the fault code 331 pops up on the controller display, understand the mixing thermistor is not functioning properly. 

Broken wire, dirty sensor probe, or the mixing thermistor itself is at fault are some culprits that cause the unit to show the error code 331. 

How To Fix: 

  • Inspect the wire connection of the mixing thermistor. It’s embedded in the water outlet connection.
  • Take a manometer and measure the resistance value of the mixing thermistor. If the mixing thermistor doesn’t give a reading of 9K ohms, clean the mixing thermistor. 
  • To clean the mixing thermistor, remove the PCB to access the mixing thermistor. Then, remove the probe sensor and clean it. 
  • If cleaning the mixing thermistor fails to resolve the error code, replace it with a new one. 

Takagi Water Heater Error Code 391

Air-fuel ratio rod failure is what the meaning of the error code 391 is. The AFR has failed if debris buildup forms on it or it gets defective. 

How To Fix: 

Complete the following procedure to clean the air-fuel ratio rod: 

  • Turn off the unit by unplugging it from the electric outlet.
  • Pull out the front cover by unscrewing the nuts.
  • Remove the three screws that hold the rod assembly in place and pull out the rod assembly. 
  • Locate the air-fuel ratio rod on the rod assembly and clean it with 100 grit sandpaper. If the AFR gets bent, replace it. 
  • Finally, reassemble the unit. 

Error Code 441

This faulty code will only pop up if your Takagi water heater is a part of an Easy-Link system. The following reasons are responsible for the unit to flash the error code 441: 

  • The wiring to the flow sensor gets broken
  • Inlet filter gets blocked by dirt and debris
  • You may forget to open the shut-off valve on the hot and cold water lines

How To Fix: 

Start with inspecting the wiring to the flow sensor. If the flow sensor wire connection comes loose or gets broken, repair the wiring. 

Next, take a look at the inlet filter for blockage. If there is any restriction, release the debris buildup by following the below procedure: 

  • Drain your tankless water heater first.
  • Remove the filter from the cold water inlet, which you can find at the bottom of the unit. 
  • Using a tiny brush, scrub the filter to remove sediments from the filter. Then, wash the filter with clean water. 
  • Insert the filter into the cold water inlet and secure it. 
  • Restore the power to the unit.

Lastly, check the shut-off valve on the hot and cold water lines and ensure you set it to the open position. 

Takagi Tankless Water Heater Error Code 991

Error code 991 on Takagi indicates imperfect combustion of the unit. This error code will be shown on the controller display for the same reasons the unit pops up the faulty code 101. 

For example, improper gas type, restriction in the intake air, and dirty burner cause the unit to not ignite properly. 

If you want to reset the error code 991, just follow the same troubleshooting steps I mentioned to erase the error code 101.  

How Do I Reset My Takagi Water Heater?

The importance of knowing how to reset the Takagi water heater is limitless. If there is a minor problem with the unit, resetting the water heater will fix it. Turns out, when an error code pops up, you can also erase the code by resetting the unit. 

To reset your Takagi Water Heater, follow the below steps: 

  • Make sure no water is flowing through the water heater. 
  • Turn off the unit and turn it on again.
  • Remove the front cover and locate the INC and DEC button on the computer board. 
  • Keep pressing both of the INC and DEC buttons simultaneously for a few seconds until the red LED lights up. 
  • Turn off the water heater and turn it on. This will reset the water heater. 


Throughout this guide, I mentioned all the reasons that cause the unit to pop up specific error codes on your Takagi Water Heater. 

What you need to do to erase an error code is- fix the issues that cause the water heater to throw a specific fault code. 

Once you resolve the issue behind the error message, reset the unit following the steps I mentioned. It will help you erase the error code and bring the water heater back into normal operating condition. 

Read Also:

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *