A.O. Smith GDHE-75 SERIES

Questions and Answers

J
Jason RamirezAug 9, 2025
What to do if A.O. Smith GDHE-75 has no hot water?
- P
  Peter NelsonAug 9, 2025
  If you're not getting enough hot water from your A.O. Smith Water Heater, start by checking the breaker, fuses, and the water heating Enable/Disable switch to ensure the unit is receiving power. Also, make sure the hot water supply valves to your fixtures are open. If the issue persists, the operating set point might be too low, or the differential setting may be too high, requiring adjustment. Check for any hot water piping leaks, open faucets, or a leaking drain valve. Another reason could be sediment or lime scale accumulation affecting the water heater's operation, in that case, flush the water heater.
B
Brooke ChristianAug 15, 2025
Why is A.O. Smith GDHE-75 water too hot?
- M
  michaelshannonAug 15, 2025
  If the water from your A.O. Smith Water Heater is too hot, the operating set point might be set too high. In this case, you should lower the operating set point. Also, check the Temperature Probe Offset settings; they might be improperly set.
C
Catherine PenaAug 25, 2025
How to fix rough starting of A.O. Smith GDHE-75?
- R
  Rachel WoodsAug 25, 2025
  For rough starting or operation issues with your A.O. Smith Water Heater, the manual suggests contacting a qualified installer or service agency for installation and service due to potential problems such as an undersized supply gas line, low or excessive gas pressure, incorrect fuel type, vent gas recirculation, excessive piping lengths, clogged intake air screens, or a blocked main burner.
L
Lonnie DoughertyAug 30, 2025
Why is my A.O. Smith GDHE-75 making noise?
- P
  Pamela GonzalezAug 30, 2025
  Normal operation of A.O. Smith Water Heater may include noises from electrical components such as the combustion blower, transformer hum, and relay contact closure.

Summary

SAFE INSTALLATION, USE AND SERVICE

GENERAL SAFETY INFORMATION

Crucial safety warnings and precautions for safe operation and installation.

INTRODUCTION

QUALIFIED INSTALLER OR SERVICE AGENCY

Requirements for qualified personnel performing installation and service.

PREPARING FOR THE INSTALLATION

Steps and considerations before starting the water heater installation process.

DIMENSIONS AND CAPACITY DATA

ROUGH IN DIMENSIONS

Diagrams and measurements for installation clearances for 50 and 75 gallon models.

FEATURES AND COMPONENTS

50 GALLON UNIT COMPONENTS

Illustrated diagram identifying key components of the 50-gallon model.

75 GALLON UNIT COMPONENTS

Illustrated diagram identifying key components of the 75-gallon model.

CONTROLS AND SWITCHES

SWITCH FUNCTIONS EXPLAINED

Explanations of key switches like blocked exhaust, intake, and blower prover.

INSTALLATION CONSIDERATIONS

LOCATING THE WATER HEATER

Guidelines for choosing a safe and appropriate location for the water heater.

COMBUSTION AIR AND VENTILATION

Requirements for adequate airflow for combustion and ventilation.

INSTALLATION REQUIREMENTS

WATER PIPING AND POWER SUPPLY

Guidelines for water piping, power, and grounding, including safety warnings.

GAS PIPING AND VALVES

MIXING VALVES

Importance and use of mixing valves to prevent scald hazards.

SEDIMENT TRAPS

Requirement for sediment traps in gas piping for safety.

GAS SUPPLY SYSTEMS

SUPPLY GAS REGULATOR REQUIREMENTS

Instructions for selecting and installing gas pressure regulators.

THERMAL EXPANSION AND WATER SYSTEMS

SPACE HEATING AND POTABLE WATER

Instructions for using the water heater in combined heating and potable water systems.

TEMPERATURE-PRESSURE RELIEF VALVE

T&P VALVE DISCHARGE REQUIREMENTS

Guidelines for safe discharge piping of the temperature-pressure relief valve.

VENTING INSTALLATION

VENT INSTALLATION CONSIDERATIONS

Factors to consider when planning and installing the vent system.

VENT PIPE TERMINATION

Guidelines for terminating vent pipes through walls or roofs.

DIRECT VENT TERMINAL INSTALLATION

INSTALLATION SEQUENCE

Step-by-step guide for the direct vent installation process.

TERMINATION CLEARANCES

SIDEWALL POWER VENT CLEARANCES

Required clearances for sidewall vent termination in power vent configurations.

SIDEWALL DIRECT VENT CLEARANCES

Required clearances for sidewall vent termination in direct vent configurations.

VERTICAL AND FLAT ROOF TERMINATION

VERTICAL VENT TERMINAL INSTALLATION

Instructions for terminating vent pipes vertically through a roof.

FLAT ROOF INSTALLATION

Requirements for vent termination on flat roofs.

CONCENTRIC VENT INSTALLATION

LOW PROFILE TERMINATION INSTALLATION

Steps for installing IPEX System 636 Low Profile Vent Kits.

LIGHTING AND OPERATION LABELS

FOR YOUR SAFETY READ BEFORE OPERATING

Crucial safety instructions to follow before operating the water heater.

OPERATING INSTRUCTIONS

Step-by-step guide for operating the water heater.

TEMPERATURE REGULATION

HOT WATER CAN SCALD

Warnings about scalding risks and how to prevent them.

HI LIMIT SWITCH (ECO)

Explanation of the high-temperature limit switch and its function.

CONTROL SYSTEM OPERATION

OVERVIEW AND NAVIGATION

Introduction to the control system and how to navigate its menus and interface.

STATUS ICONS AND OPERATING STATES

STATUS ICONS DESCRIPTIONS

Descriptions of icons displayed on the control system for operational status.

OPERATING STATES DESCRIPTIONS

Table describing the different operational states of the water heater.

USER SETTINGS AND MENUS

OPERATING SET POINT ADJUSTMENT

How to adjust temperature settings and differential for optimal performance.

TROUBLESHOOTING

CURRENT FAULT AND HISTORY

Displays current error messages, logs, and how to reset system lockouts.

INSTALLATION CHECKLIST

A checklist of critical installation requirements to prevent operational issues.

SEQUENCE OF OPERATION

SEQUENCE OF OPERATION FLOW CHART

Visual flow chart detailing the water heater's operational sequence.

OPERATIONAL PROBLEMS

ROUGH STARTING AND NO HOT WATER

Troubleshooting common issues with burner operation and hot water supply.

FAULT AND ALERT MESSAGES

IGNITION AND EXHAUST FAULTS

Lists ignition failure and blocked exhaust messages with causes.

BLOWER, INTAKE, ECO, AND ANODE FAULTS

Lists fault/alert messages for blower, intake, ECO, and anode voltage issues.

WIRING DIAGRAM

LIMITED RESIDENTIAL GAS WARRANTY

Terms and conditions that apply to the water heater warranty.