Bosch GWH 635 ES User Manual

Bosch GWH 635 ES

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GWH-635-ES

INDOOR MODEL

Temperature Modulated with Electronic Ignition

Suitable for heating potable water only - Not approved for space heating purposes

(Intended for variable flow applications)

GWH-635-ES-N - Natural Gas

GWH-635-ES-L - Liquefied Petroleum (LP) Gas

6 720 607 072 US (05.12) AL

Warning: If the information in this manual is not

followed exactly, a fire or explosion may result

causing property damage, personal injury or death.

Do not store or use gasoline or other flammable

vapor and liquids in the vicinity of this or any other

appliance.

Improper installation, adjustment, alteration,

service or maintenance can cause injury or

property damage. Refer to this manual. For

assistance or additional information consult a

qualified installer, service agency or the gas

supplier.

In the Commonwealth of Massachusetts this

product must be installed by a licensed plumber or

gas fitter.

Upon completion of the installation, these

instructions should be handed to the user of the

appliance for future reference.

What to do if you smell gas

• Close gas valve. Open windows.

• Do not try to light any appliance.

• Do not touch any electrical switch; do not use any

phone in your building.

• If you cannot reach your gas supplier, call the fire

department.

• Immediately call your gas supplier from a neighbor’s

phone. Follow the gas supplier’s instructions.

• Installation and service must be performed by a

qualified installer, service agency or the gas supplier.

Table of Contents

Other manuals for Bosch GWH 635 ES

Service Bulletin Booklet20 pages

Questions and Answers:

J
Joseph AdamsJul 30, 2025
Why won't the burners ignite on my Bosch Water Heater when I turn on the hot water?
- K
  kaufmanhectorJul 30, 2025
  If the burners on your Bosch Water Heater don't ignite when you turn on the hot water, it could be due to several reasons. First, ensure the cold water inlet is connected to the correct side of the heater. Second, the water flow rate might be too low; a minimum of 0.8 gallon/minute (3 l/m) is needed to activate the heater. Third, a dirty cold water inlet filter screen can cause this issue; remove and clean it, also check the faucet aerator screens. Finally, a crossover in the plumbing could be the problem. To check this, shut off the cold water supply to the heater and individually open each hot water tap; there should be no water flowing under constant pressure.
D
Duane NunezAug 4, 2025
How to adjust the temperature if the water is too hot in my Bosch Water Heater?
- V
  Valerie GonzalesAug 4, 2025
  If the water from your Bosch Water Heater is too hot, the temperature selection might be set too high. You should lower the temperature adjustment either on the heater itself or via the wireless remote, if applicable.
B
brandon55Aug 10, 2025
What to do if Bosch GWH 635 ES Water Heater water is not hot enough?
- M
  Mckenzie SmithAug 10, 2025
  If the water from your Bosch Water Heater isn't hot enough, the temperature selection may be set too low; increase the temperature adjustment on the heater. Also, the BTU input could be too low due to inadequate gas line sizing. Check specifications in chapter 2.10 - 2.12. The GWH-635-ES requires adequate gas pressure to reach desired temperatures. To compensate for inadequate gas supply or lack of gas pressure, the GWH-635-ES will effectively reach the selected output temperature by reducing the hot water flow rate.
A
Ashley JohnsonAug 14, 2025
Why is the water flow/pressure low in my Bosch GWH 635 ES?
- J
  Joseph WilliamsAug 15, 2025
  Low water flow or pressure in your Bosch Water Heater can occur for several reasons. It might be because too many hot water applications are being used at once, exceeding the heater's capacity. The GWH-635-ES model effectively supports two 2.0-2.5 gpm shower heads simultaneously or multiple sink applications, but greater demands will reduce flow. Inadequate gas line sizing leading to low BTU input could also be the cause, so refer to specifications in chapter 2.10 - 2.12. Another potential issue is a dirty cold water inlet filter screen, which requires removal and cleaning, and also check faucet aerator screens.
W
Wayne EdwardsAug 19, 2025
Why does the hot water temperature fluctuate in my Bosch GWH 635 ES?
- D
  Donna GriffinAug 19, 2025
  If the hot water temperature fluctuates or the unit deactivates in your Bosch Water Heater, it could be due to unbalanced pressure in the water lines; a pressure balance valve may help. Alternatively, if the outlet water temperature is set too high, the heater can produce temperatures that are excessively hot.
I
Isaiah FrancoAug 25, 2025
Why is my Bosch GWH 635 ES Water Heater burner noisy during operation?
- S
  smithnicoleAug 25, 2025
  If your Bosch Water Heater's burner or heater is noisy during operation, the CO2 range might be out of adjustment. Ensure the cover is in place to confirm CO2 readings, as operating the heater with the cover removed may cause a noisy or unstable burner.

Bosch GWH 635 ES Specifications

General

Type	Tankless
Fuel Type	Natural Gas
Energy Factor	0.82
Ignition Type	Electronic
Maximum Temperature	140°F
Gas Connection	1/2 inch
Water Connection	1/2 inch

Summary

Warning and Safety Precautions

What to Do If You Smell Gas

Emergency steps to take in case of a gas leak.

Fire and Explosion Prevention

Guidelines to prevent fire and explosion hazards.

Appliance Details

Features

Lists the main attributes and parts of the water heater.

Specifications (Technical Data)

Details technical data like capacity, output, input, and efficiency.

Installation Requirements: Dimensions and Clearances

Dimensions

Specifies the physical size of the appliance.

Minimum Installation Clearances

Outlines required space around the appliance.

Installation Requirements: Safe Operation and Location

General Rules for Safe Operation

Outlines essential guidelines for safe and proper use.

Proper Location for Installing Your Heater

Guidance on selecting an appropriate installation site.

Installation Requirements: Mounting and Air Supply

Mounting Installation

Steps for securely mounting the water heater.

Combustion Air Requirements

Details on providing adequate combustion air.

Installation Requirements: Venting System

Venting System Requirements

Critical information on exhaust venting systems.

Installation Requirements: Gas Piping

Gas Piping and Connections

Procedures for gas supply connection, including sizing.

Installation Requirements: Gas Pressure

Measuring Gas Pressure

Procedures for measuring gas pressure.

Installation Requirements: Water Connections

Water Connections and PRV Installation

Details on connecting water lines and installing the pressure relief valve.

Installation Requirements: Electrical and Initial Operation

Electrical Connections

Details on wiring requirements and safe electrical grounding.

Initial Operating Instructions

Basic steps for preparing the unit for operation.

Operation Instructions

Power On/Off

How to turn the appliance on and off.

Temperature Selection

Steps for setting the desired hot water temperature.

Advanced Operation Features

Remote Control and Programming

Information on using the optional remote control and programming functions.

Reset Button and Locked Condition

Explains how to use the reset button and the locked status.

Maintenance and Service

Annual Checks and Front Cover Removal

List of components for yearly inspection and cover removal steps.

Troubleshooting

Burner Ignition and Water Temperature Issues

Addresses burner ignition and water temperature problems.

Troubleshooting Continued

Low Water Flow, Gas Supply, and Noise Issues

Diagnoses issues related to water flow, gas supply, and operational noise.

Electrical Diagram

Electrical Scheme Overview

Diagram illustrating electrical wiring.

Functional Scheme

Operational Logic Diagram

Diagram showing the control logic of the appliance.

Interior Components and Parts List

Interior Components Overview

Visual identification of internal parts.

Components Diagram and Parts List

Detailed Components Diagram

Exploded view of the appliance's internal components.

Parts List

A comprehensive list of part numbers and descriptions.

CO2 Adjustment

Measuring and Adjusting CO2 Levels

Steps for measuring and adjusting CO2 levels.

Environmental Protection

Water Resource Conservation

Advice on conserving water through efficient usage.

Limited Warranty

Warranty Terms and Claim Process

Warranty coverage, exceptions, and how to make a claim.

Installer Checklist

Final Installation Checks and Handover

Checklist for installers upon completion of installation.

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