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Bosch 125FX LP - User Manual

Bosch 125FX LP
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WARNING: 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.
Upon completion of the installation, these instructions
should be handed to the user of the appliance for future
reference.
In the Commonwealth of Massachusetts this product
must be installed by a licensed plumber or gas fitter.
FEATURING: Electronic Ignition and Power Venting
INSTALLATION AND OPERATING INSTRUCTIONS FOR AUTOMATIC
INSTANTANEOUS TYPE WATER HEATER FOR USE WITH NATURAL AND
LIQUEFIED PETROLEUM GAS
MODEL 125FX LP and 125FX NG
(Flow Modulated with Electronic Ignition and Power Venting)
Suitable for heating potable water only
Not approved for space heating purposes
Intended for variable flow applications with steady cold water inlet temperatures
WARNING
If the information in this manual is not followed exactly. A
fire or explosion may result causing property damage,
personal injury or death.
FOR YOUR SAFETY
Do not store or use gasoline or other flammable,
combustible or corrosive vapors and liquids in the vicinity
of this or any other appliance.
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.
- 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.
Specifications............................................. Page 2
Rules for safe operation ........................... Page 4
Locating the Heater .................................. Page 4
Combustion Air Requirements ................ Page 5
Mounting the Heater ................................. Page 6
Venting the Heater .................................... Page 7
Gas Connections ....................................Page 10
Water Connections .................................Page 12
Electrical Connections ...........................Page 13
Safety before turning on the heater .... Page 14
Lighting and Operating instructions ....Page 14
Setting water temperature ..................... Page 14
Maintenance & Service.......................... Page 15
Trouble Shooting...................................... Page 16
Diagram of AquaStar ............................. Page 20
Components and Parts List .................. Page 22
Warranty ................................................... Page 25
TABLE OF CONTENTS
6 720 606 601 US (04.10) AL

Table of Contents

Other manuals for Bosch 125FX LP

Preview: Installation And Operating Instrictions
Installation And Operating Instrictions20 pages

Questions and Answers

  • K
    karenturnerAug 16, 2025
    What to do if sparks appear at pilot, but pilot and burners won't ignite on Bosch 125FX LP?
    • R
      Richard HamptonAug 16, 2025
      If sparks appear at the pilot when you turn on the hot water tap, but the pilot and burners won't ignite, try these steps: * Bleed air from the gas line by repeatedly turning the hot water faucet on and off until the air is cleared. * Ensure the gas cock on the gas line is fully open. * The pilot orifice or gas filter may need cleaning. * The water valve assembly should be checked. * Measure millivoltage at pilot electrovalve. * Check wire connections and test operation of control box.
  • O
    Olivia EvansAug 18, 2025
    What to do if pilot lights, but burners will not come on my Bosch 125FX LP?
    • R
      ricecarrieAug 19, 2025
      If the pilot light on your Bosch Water Heater lights, but the burners won't come on, check that the unit is plugged in and that the sensors for the flue gases are secure. Also, check wire connections and test operation of control box.
  • K
    kellertonyAug 25, 2025
    Why do the main burners go out during hot water use on my Bosch Water Heater?
    • J
      julie20Aug 26, 2025
      If the main burners go out during hot water use with your Bosch Water Heater, it could be due to: 1. Deficient exhaustion of flue gases. Check that the vent is correct and clear of any obstructions. 2. Flow rate diminished below activation rate. Be certain that water flow is not less than the required amount to activate the heater. 3. Unbalanced pressure in waterlines. Make sure faucet aerators or shower heads are free of minerals. 4. ECO (overheat sensor) tripped due to overheating. Do not feed preheated water to this water heater. 5. Minimum inlet pressure on well pressure tank is inadequate. Check the inlet water pressure.
  • T
    Tyler VazquezAug 28, 2025
    Why is the water not hot enough on my Bosch Water Heater?
    • P
      pereztammyAug 28, 2025
      If your Bosch Water Heater's water is not hot enough, try the following: * Turn the temperature selector knob clockwise (to the right). * Make sure your main gas line is fully opened. * Check for mixing valve or plumbing crossover. * If the internal water valve parts are damaged from water quality or use, or there is evident corrosion where the water valve and gas valve connect, then immediate service is needed.
  • G
    Gina BrownAug 30, 2025
    Why does the hot water temperature fluctuate or unit deactivate on my Bosch Water Heater?
    • C
      charlene03Aug 30, 2025
      If the hot water temperature from your Bosch Water Heater fluctuates or the unit deactivates, ensure faucet aerators or shower heads are free of minerals. If the inlet water temperature to the water heater is very warm the heater can produce temperatures that may be found to be too hot. Also check the inlet water pressure.
  • I
    ikimSep 2, 2025
    How to fix water that is too hot in my Bosch 125FX LP Water Heater?
    • C
      Carla BeardSep 2, 2025
      If your Bosch Water Heater's water is too hot, turn the temperature adjustment knob counter-clockwise (to the left) to lower the maximum water temperature. Reduce inlet gas supply to lower the heaters degree rise. Remove screen and clean it.
  • K
    Kathleen JonesSep 5, 2025
    Why does the pilot spark continuously on my Bosch 125FX LP even when no water is running?
    • C
      Christopher ObrienSep 6, 2025
      If the pilot electrode sparks continuously even when no water is running, the microswitch screw to the water valve likely needs adjustment.
  • K
    Kenneth HammondSep 9, 2025
    What to do if fan circulates when hot water is shut off on Bosch 125FX LP?
    • N
      Nancy ChristianSep 9, 2025
      Check adjustment of microswitch.
  • J
    Julie LittleSep 12, 2025
    What causes the fan to operate without water flow in Bosch 125FX LP?
    • W
      William WallaceSep 12, 2025
      To address a fan that operates without water flow in your Bosch Water Heater, unplug the heater and first check that all electrical and electronic connections in the heater are clean and tight. Check adjustment of microswitch. Control box may need to be replaced.
  • J
    James KnappNov 20, 2025
    How to troubleshoot no spark at the pilot in Bosch 125FX LP Water Heater?
    • A
      Alexander SimonNov 20, 2025
      If there is no spark at the pilot of your Bosch Water Heater, make sure the On/Off switch is in the ”On” position. The On/Off switch is located behind the flipdown cover. Also, be certain that all electrical connections are clean, tight, and free of any moisture. When temperature adjustment knob is turned all the way clockwise, the AquaStar model 125FX requires 1/2 gallon per minute flow to activate the heater. Check the viability of the fuse and replace if necessary. Clean water inlet filter screen. To confirm there is no cross-over in the plumbing, shut off the cold water supply to the AquaStar water heater and open a hot water faucet. If you do not hear a click when a tap is opened, the microswitch needs to be adjusted. Make sure cold water inlet connection is on the right side when you...

Summary

General Safety and Installation Warnings

What to Do If You Smell Gas

Immediate actions to take if a gas leak is detected to prevent fire or explosion.

Installation and Service Requirements

Mandates qualified personnel for installation, service, and adherence to codes.

Principle of Operation

AquaStar 125 FX Specifications

Gas Input and Flow Rates

Details the BTU input, flow rates, and pressure requirements for different gas types.

Physical and Electrical Specifications

Covers dimensions, weight, water connections, and electrical power requirements.

Installation Clearances

Clearances from Combustible Materials

Specifies minimum distances required between the unit and combustible surfaces for safe installation.

General Rules for Safe Operation

Installation Location Guidelines

Provides essential rules for safe placement, ventilation, and combustion air supply.

Combustion Air Requirements

Air Supply for Confined Spaces

Details the specific ventilation openings needed for units installed in confined areas.

Air Supply for Unconfined Spaces

Explains how infiltration provides adequate air in unconfined spaces.

Mounting Installation

Wall Mounting Procedures

Step-by-step instructions for securely attaching the heater to a wall, including support board use.

Venting Requirements

Vent Pipe Specifications and Clearances

Covers vent pipe material, diameter, sealing, length limits, and required clearances.

Freeze Prevention and Flue Gas Sensor

Addresses freeze protection measures and the functional test for the flue gas sensor.

Venting Guide Suggestions

Horizontal Side Wall Venting Example

Illustrates a common horizontal venting configuration with an approved terminal.

Side Wall Vent Terminal Locations

Vent Terminal Clearance Rules

Specifies exact clearance requirements for vent terminals exiting through side walls.

Gas Connections and Regulator Installation

Gas Line Sizing and Pressure Settings

Gas Piping Capacity Charts

Natural Gas Pipe Capacity

Table showing maximum capacity of black iron pipe for natural gas based on size and length.

LP Gas Pipe Capacity

Table showing maximum capacity of black iron and copper pipe for LP gas based on size and length.

Water Connections

Connecting Water Lines and PRV

Instructions for plumbing connections, including water valve servicing and PRV installation.

Electrical Connections and Wiring Diagram

Electrical Connection Guidelines

Covers power supply, grounding, and safety precautions for electrical connections.

Wiring Diagram for AQ 125 FX

Illustrates the internal electrical connections and identifies all components within the wiring system.

Operating and Safety Procedures

Initial System Setup and Safety Checks

Covers filling the system, safety precautions, gas leak procedures, and basic operation.

Lighting and Turning Off the Heater

Details the process for lighting the pilot and main burners, and how to shut down the unit.

Setting Water Temperature

Explains how to adjust the hot water temperature using the control knob.

Maintenance and Service Procedures

Routine Maintenance Tasks

Details annual checks for the vent system, water valve, pilot assembly, and main burner.

Pilot Flame Adjustment and Cleaning

Guidance on checking pilot flame characteristics and cleaning the pilot burner and orifice.

Troubleshooting Common Issues

No Spark or Pilot Ignition Failure

Addresses problems like no spark, insufficient water flow, or clogged filters preventing ignition.

Advanced Troubleshooting

Burner Ignition and Operation Problems

Solutions for issues where the pilot lights but burners don't, or main burners shut off.

Water Temperature and Unit Performance Issues

Water Temperature Too Hot or Too Cold

Diagnoses and resolves problems with water temperature being too high, too low, or fluctuating.

Exhaust Fan and Water Flow Malfunctions

Troubleshoots issues with the exhaust fan operation and the unit shutting off during use.

AquaStar 125 FX External Component Diagram

Component Identification Key

A labeled diagram identifying all external parts of the AquaStar 125FX unit.

Interior Components Diagram and Parts List

Internal Parts Identification

Provides a detailed diagram and list of all internal components of the AquaStar 125FX.

Bosch 125FX LP Specifications

General IconGeneral
BrandBosch
Model125FX LP
CategoryWater Heater
LanguageEnglish

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