Takagi AT-D3U-IN - User Manual

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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
daniel67Aug 12, 2025
Why does my Takagi AT-D3U-IN not ignite when water runs through it?
- G
  George DiazAug 12, 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.
R
Robert AndrewsAug 16, 2025
Why is my Takagi AT-D3U-IN Water Heater water not hot enough?
- J
  Joel RochaAug 16, 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.
N
nbrownAug 20, 2025
What to do if hot water is not available from my Takagi AT-D3U-IN Water Heater?
- A
  Alexander MurrayAug 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.
T
trandavidAug 25, 2025
How to get hot water faster from my Takagi AT-D3U-IN?
- T
  trujillonicoleAug 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
Anthony SweeneyAug 27, 2025
Why is the hot water temperature fluctuating with my Takagi Water Heater?
- M
  Michael JohnstonAug 27, 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.
A
Ashley AndersonAug 31, 2025
What to do if my Takagi AT-D3U-IN's hot water turns cold and stays cold?
- M
  martin29Aug 31, 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.
R
Ralph BoothSep 4, 2025
Why is the display not working on my Takagi Water Heater controller?
- T
  Terry MeyerSep 4, 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.
T
Thomas StewartSep 7, 2025
Why does the fan motor keep spinning on my Takagi AT-D3U-IN Water Heater after it stops?
- J
  Jimmy NashSep 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-D3U-IN Specifications

General

Brand	Takagi
Model	AT-D3U-IN
Category	Water Heater
Language	English

Summary

Product Specifications and Safety Guidelines

Manual Introduction and Models

Overview of the manual, water heater models, and core function.

Safety Guidelines

Critical safety information, definitions, and general precautions for installation and use.

Installation Guide

Clearances and Venting

Required physical clearances and essential venting instructions for safe installation.

High-Altitude and Installation Warnings

Prohibitions, warnings, and altitude adjustments for installation locations.

Gas, Water, and Electrical Connections

Guidelines for connecting gas supply, water lines, and electrical power.

System Configurations

Setup for remote controllers, Easy-Link, and Multi-Unit systems.

Operation and Maintenance

Initial and Normal Operation

Steps for safe startup, normal use, and controller functions.

Temperature and Flow Settings

Adjusting water temperature and understanding flow rate impact.

Freeze Protection and Maintenance

Features to prevent freezing and routine maintenance procedures.

Troubleshooting and Reference

Problem Diagnosis and Error Codes

Identifying and resolving common issues and interpreting error codes.

Components, Parts, and Warranty

Diagrams of components, parts list, performance charts, and warranty details.

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