Takagi AT-KJr3U-IN User Manual

Takagi AT-KJr3U-IN

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Gas Tankless Water Heater

TM

Suitable for combination potable water heating

and space-heating

Please refer to local codes for space-heating compliance.

FEATURING

 • ENDLESSHOTWATER

 • ON-DEMANDUSAGE

 • COMPACT,SPACESAVING

 • ENERGYCONSERVATION

 • COMPUTERIZEDSAFETY

 • NOPILOTLIGHT

 • ComplieswithSCAQMDRule

1146.2forNOxemissionsrequire-

mentof14ng/Jor20ppm

 • FIELDGASCONVERTIBLE

 • EASY-LINKSYSTEMAND

MULTI-UNITSYSTEM

(510U (AT-D3U-IN/OS) only)

Ifyouhaveanyquestions,please

callorwriteto:

500TennesseeWaltzParkway

AshlandCity,TN37015

TollFree:1-877-737-2840

On-Demand Water Heater

Installation Manual and Owner’s Guide

- Do not store or use gasoline or other

flammablevaporsandliquidsinthevicinity

ofthisoranyotherappliance.

- WHATTODOIFYOUSMELLGAS

 • Donottrytolightanyappliance.

 • Donottouchanyelectricswitch,donot

useanyphoneinyourbuilding.

 • Immediatelycallyourgassupplierfrom

aneighbor'sphone.Followthegas

supplier'sinstructions.

 • Ifyoucannotreachyourgassupplier,call

thefiredepartment.

- Installation and service must be performed

byaqualifiedinstaller,serviceagencyorthe

gassupplier.

WARNING

If the information in these

instructions is not followed

exactly,afireorexplosionmay

resultcausingpropertydamage,

personalinjuryordeath.

ANSI Z21.10.3 ・ CSA 4.3

510U (AT-D3U-IN/OS)

only

Models

• 110U Outdoor (AT-KJr3U-OS)

• 310U Outdoor (AT-K5U-OS)

• 510U Outdoor (AT-D3U-OS)

• 110U Indoor (AT-KJr3U-IN)

• 310U Indoor (AT-K5U-IN)

• 510U Indoor (AT-D3U-IN)

Series 200

Table of Contents

Questions and Answers:

D
Danielle RiveraAug 13, 2025
Why does my Takagi AT-KJr3U-IN not ignite when water runs through it?
- M
  Michelle FitzgeraldAug 13, 2025
  If your Takagi Water Heater doesn't ignite when water flows through it, ensure the flow rate is over 0.5 GPM. Check the filter on the cold water inlet for any blockages. Inspect for reverse or cross connections. If you're using a remote controller, ensure it's powered on. Verify that the inlet water temperature isn't too close to the set temperature. Confirm the gas supply is turned on and that the unit has power, with the power button on either the controller or inside the water heater activated.
C
Cheryl MartinAug 17, 2025
Why is my Takagi AT-KJr3U-IN Water Heater water not hot enough?
- K
  kaitlyn08Aug 17, 2025
  If your Takagi Water Heater isn't producing hot enough water, several factors could be the cause. Begin by comparing the flow and temperature using the charts. Check for cross plumbing between cold and hot water lines. Ensure the gas supply valve is fully open and the gas line is properly sized, with the supply pressure within specified limits. Verify that the set temperature isn't too low and that the Easy Link or Multi-Unit system is correctly configured.
B
Breanna KimAug 20, 2025
What to do if hot water is not available from my Takagi Water Heater?
- B
  Blake SmithAug 20, 2025
  If you're not getting hot water from your Takagi Water Heater when you open a fixture, check the following: ensure the unit has a 120 VAC, 60 Hz power supply and that the power button on the controller or inside the water heater is turned on. Also, verify that both the gas and water supply valves are fully open, and the filter on the cold water inlet is clean. Make sure the hot water fixture is sufficiently open to draw at least 0.5 GPM through the water heater, and check that the unit is not frozen. Finally, inspect for cross plumbing between the hot and cold water lines, and ensure the Easy Link or Multi-Unit system is set up correctly.
B
Bruce DiazAug 25, 2025
How to get hot water faster from my Takagi Water Heater?
- M
  mcurryAug 25, 2025
  The time it takes for hot water to reach your fixtures from your Takagi Water Heater depends on the length of piping and the pipe size between the two. The longer the distance or the bigger the pipes, the longer it will take to get hot water. If you want hot water more quickly, consider a hot water recirculation system.
A
Alexander LeeAug 29, 2025
Why is the hot water temperature fluctuating with my Takagi Water Heater?
- R
  robertsmithAug 29, 2025
  If you are experiencing temperature fluctuations with your Takagi Water Heater, ensure the filter on the cold water inlet is clean. Check that the gas line is properly sized and the supply gas pressure is within specified limits. Also, check for any cross connection between the cold and hot water lines, and verify that the Easy Link or Multi-Unit system is set up correctly.
T
Tara BellSep 1, 2025
What to do if my Takagi Water Heater's hot water turns cold and stays cold?
- S
  Shirley WilsonSep 1, 2025
  If the hot water from your Takagi Water Heater turns cold and stays cold, first check if the flow rate is enough to keep the water heater running. If you have a recirculation system installed, ensure the recirculation line has enough check valves. Also, verify that the gas supply valve is fully open and the filter on the cold water inlet is clean. Lastly, ensure that your fixtures are clean of debris and obstructions.
D
David SmithSep 4, 2025
Why is the display not working on my Takagi Water Heater controller?
- J
  Jamie BriggsSep 5, 2025
  If the built-in or remote controller of your Takagi Water Heater doesn't display anything when turned on, first ensure the unit is receiving power. For the remote controller, check that the connection to the unit is correct. Note that when the built-in controller is turned on, the STAND BY LED should be lit. Also, if the unit hasn't been used for five minutes or more, the display might turn off to save energy. Finally, in an Easy-Link System, only the parent unit's controller will display the set temperature.
M
Morgan UnderwoodSep 8, 2025
Why does the fan motor keep spinning on my Takagi AT-KJr3U-IN after it stops?
- D
  David ClaytonSep 8, 2025
  It is normal for the fan motor of your Takagi Water Heater to continue running for 15 to 70 seconds after operation has stopped. This allows for quick re-ignition and purges exhaust gas from the flue.

Takagi AT-KJr3U-IN Specifications

General

Type	Tankless Water Heater
Fuel Type	Natural Gas
Dimensions	20.3" x 13.8" x 6.7"
Weight	38 lbs
Flow Rate	6.6 GPM
Maximum Temperature	140°F
Ignition Type	Electronic
Venting	Direct Vent

Summary

Specifications

Safety Guidelines

Safety Definition

Defines safety terms like DANGER, WARNING, CAUTION, and NOTICE for hazard communication.

Installation

Clearances

Warning for Installations

Venting Instructions

For Indoor Models

Details on venting for indoor models, including general rules, air intake, and direct venting.

General Rules for Air Intake

Guidelines for obtaining combustion air for the water heater.

Direct Venting Installation

Specific instructions for direct venting installations, including pipe length and termination.

Combustion Air Supply

Vent Length and No. of Elbows

Gas Supply and Pipe Sizing

Water Connections

Pressure Relief Valve

Details on the requirement, installation, and function of the pressure relief valve.

Electrical Connections

Temperature Remote Controller

Easy-Link System

General Easy-Link System Information

Overview of the Easy-Link System, its capabilities, and compatibility.

Easy-Link Connection Procedures

Step-by-step guide for connecting units in an Easy-Link System.

Multi-Unit System

Initial Operation

Operating Safety

Operating Instructions

Instructions on how to safely start and operate the water heater.

To Turn Off Gas to Appliance

Procedure for safely shutting off the gas supply to the appliance.

Normal Operation

Built-in Controller and Remote Controller

Explanation of the built-in and remote controller displays and functions.

Temperature Settings

Maintenance and Service

Troubleshooting

General Troubleshooting

General troubleshooting for common issues like water temperature and flow.

Error Codes

Fault Analysis of Error Codes

Detailed breakdown of error codes, their causes, and diagnostic steps.

Components Diagram

Limited Warranty

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