Bosch WT Series User Manual (English)

Questions and Answers:

C
Cindy FordAug 19, 2025
How to troubleshoot a Bosch WT when the entire unit does not run?
- K
  kelleyelizabethAug 19, 2025
  If your entire Bosch Heat Pump unit isn't running, start by ensuring the power supply is on and the disconnect is closed. If that's not the issue, check for a blown fuse and replace it or reset the circuit breaker, making sure you use the correct fuses. Also, verify that the voltage supply meets the minimum specified on the unit's data plate. If the voltage is too low, contact your local power company.
R
Ryan TuckerAug 21, 2025
Why is my Bosch Heat Pump providing insufficient cooling or heating?
- M
  Ms. Kristine MarshallAug 21, 2025
  If your Bosch Heat Pump is providing insufficient cooling or heating, several factors could be at play. Start by recalculating the heating or cooling loads to ensure the unit is properly sized. Inadequate fluid flow could also be the cause. Check for a low refrigerant charge, which can lead to inefficient operation. Inspect the compressor for defects. Also, a defective reversing valve can cause refrigerant bypass. Compare unit operating pressures to the pressure/temperature chart. Examine the TXV for restrictions or defects. Finally, the refrigerant system might be contaminated. In that case, reclaim the refrigerant, replace the filter dryer, evacuate the system, and recharge with the factory-recommended charge.
M
Matthew AllenAug 23, 2025
How do I troubleshoot no flow or low flow in my Bosch Heat Pump?
- D
  dixonjulieAug 25, 2025
  If you're experiencing no flow or low flow in your Bosch Heat Pump, check the power supply first. Ensure the on/off switch is in the “ON” position. Verify the compressor contactor is engaged. Inspect for broken or loose wires and repair or tighten them. Purge any air from the piping system. If the pump shaft or impeller is stuck, remove the pump cartridge and clean it. If the pump is defective, replace it. Finally, check for kinked or undersized water piping and repair any kinks, ensuring the line size is appropriate.
M
Michael HolmesAug 26, 2025
What to do if my Bosch WT unit turns off on high pressure control?
- X
  xavier52Aug 26, 2025
  If the Bosch Heat Pump unit shuts off due to high pressure control, the discharge pressure might be too high. In cooling mode, ensure adequate water flow and that the entering water temperature isn't too warm, and check for scaled or plugged condenser. In heating mode, check for sufficient load side fluid flow. Also, the unit might be overcharged with refrigerant, so reclaim refrigerant, evacuate, and recharge with the factory-recommended charge. Finally, inspect the high-pressure switch for defects or improper calibration.
J
john16Aug 28, 2025
Why does my Bosch WT unit short cycle?
- F
  fburchAug 28, 2025
  If your Bosch Heat Pump is short cycling, it could be due to several reasons. The unit might be oversized, requiring a recalculation of heating or cooling loads. The thermostat might be installed near a supply air grill, so relocate it. You might also need to readjust the heat anticipator. Check the wiring and controls for a defective or improperly calibrated low-pressure switch.
K
Kimberly JohnsonAug 30, 2025
What to do if my Bosch WT Heat Pump unit turns off on low pressure control?
- J
  Jacqueline JohnsonAug 30, 2025
  If your Bosch Heat Pump unit shuts off due to low pressure control, the suction pressure might be too low. In cooling mode, ensure adequate source side fluid flow and that the entering water temperature isn't too cold. In heating mode, check for sufficient water flow and that the entering water temperature isn't too cold, and check for a scaled or plugged condenser. Also, the unit might be low on refrigerant, so check for leaks, repair, evacuate, and recharge with the factory-recommended charge. Finally, inspect the low-pressure switch for defects or improper calibration.
J
jasmine10Sep 1, 2025
What does Yellow "Alert" Flash Code 5 mean on my Bosch WT Heat Pump?
- S
  Shannon HarveySep 1, 2025
  If your Bosch Heat Pump displays a Yellow "Alert" Flash Code 5, it indicates an open circuit. Check if the outdoor unit power disconnect is open. Inspect the compressor circuit breaker or fuses for being open. Verify the compressor contactor for failure. Check wiring and connectors, and also check for low pilot voltage at the compressor contactor coil. A high-pressure switch might be open and require manual reset. Look for open circuits in the compressor supply wiring or connections. Consider unusually long compressor protector reset time due to extreme ambient temperature. Damaged compressor windings can also cause this, so check the compressor motor winding resistance.
E
emmamitchellSep 3, 2025
What does Yellow "Alert" Flash Code 4 mean on my Bosch WT?
- T
  tiffany14Sep 3, 2025
  If your Bosch Heat Pump displays a Yellow "Alert" Flash Code 4, it indicates a locked rotor. Check if the run capacitor has failed. Verify the line voltage and contact the utility if the voltage at the disconnect is low. Ensure there isn't excessive liquid refrigerant in the compressor. Check if the compressor bearings are seized and measure the compressor oil level.
J
Jeffrey MarshallSep 5, 2025
What does Yellow "Alert" Flash Code 6 mean on my Bosch WT?
- M
  megan87Sep 6, 2025
  If your Bosch Heat Pump displays a Yellow "Alert" Flash Code 6, it indicates an open start circuit. Check if the run capacitor has failed. Inspect the compressor start wiring and connections, ensuring they are properly connected to the compressor "S" terminal. Damaged compressor start winding can also cause this, so check the compressor motor winding resistance.
C
colinbushSep 7, 2025
What does Yellow "Alert" Flash Code 7 mean on my Bosch WT?
- E
  Erin WangSep 7, 2025
  If your Bosch Heat Pump displays a Yellow "Alert" Flash Code 7, it indicates an open run circuit. Inspect the compressor run wiring and connections, ensuring they are properly connected to the compressor "R” terminal. Damaged compressor run winding can also cause this, so check the compressor motor winding resistance.

Bosch WT Series Specifications

General

Brand	Bosch
Model	WT Series
Category	Heat Pump
Language	English

Summary

Key to Symbols and Safety Warnings

Warnings and Important Information

Defines warning symbols and important information indicators.

Safety Warnings and Precautions

Details hazards and safety precautions for installation and service.

Refrigerant Handling Notice

Specifies refrigerant recovery requirements by certified technicians.

Construction Use Prohibition

Advises against using units during construction to avoid damage.

Model Nomenclature

WT Model Nomenclature

Explains the coding system for WT model identification.

WW Model Nomenclature

Explains the coding system for WW model identification.

Standard WW/WT Package Overview

General Description and Certifications

Details performance, certifications, and operating temperature ranges.

Moving, Storage, and Inspection

Guidelines for handling, storing, and initially inspecting the unit.

Location and Piping Requirements

Recommendations for unit placement and piping size.

Installation Guidelines

Instructions for mounting the unit level on a vibration pad.

Electrical and Piping Considerations

Water Piping Recommendations

Guidance on water line insulation, valve types, and flow rates.

Electrical Safety and Wiring

Adherence to codes and proper wiring practices.

Voltage and Circuit Protection

Proper voltage supply and circuit breaker requirements.

UPM Control and Safety Devices

UPM I and UPM II Controller Diagrams

Diagrams illustrating safety devices on UPM controllers.

Thermostat Malfunction Light Connections

Instructions for connecting thermostat malfunction lights.

Safety Controls and UPM Operation

Pressure Switches and Freeze Protection

Details on high/low pressure switches and freeze protection.

UPM Board Settings and Features

Factory default settings and features of the UPM board.

UPM Timers and Protection Functions

Explanation of anti-short cycle, random start, and brownout protection.

Malfunction Output and 24VAC Wiring

Configuration of malfunction output and 24VAC wiring.

UPM Functions and Options

Display Output and Test Mode

Functionality of display output and test dip switch.

Freeze Sensor and Lockout Reset

Freeze sensor operation and lockout reset procedures.

Heat Recovery Package (HRP) Introduction

Overview of the HRP option for heating potable water.

Heat Recovery Package (HRP) Details

HRP Freezing Precautions and Flow Proving

Preventing HRP freezing and DPS water flow proving.

Pump Relay and Comfort Alert Module

Function of pump relay and Comfort Alert Module.

HRP Water Tank Preparation and Piping

Steps for preparing the water tank and HR piping.

HRP Water Tank Refill Procedure

Procedure for refilling the water tank after service.

Sequence of Operation

Initial Start-Up Procedure

Steps for initial system startup and checks.

Cooling Mode Operation

Operation sequence for cooling mode with thermostat calls.

Heating Mode Operation

Operation sequence for heating mode with thermostat calls.

Sequence of Operation Flow

Operational Flow Diagram

Visual representation of the unit's operational sequence.

Application Considerations

Well Water Systems

Considerations for well water quality and piping.

Cooling Tower/Boiler Systems

Operational considerations for cooling tower/boiler systems.

Application Considerations

Air Elimination and Piping Notes

Importance of air removal and piping connection notes.

Geothermal Systems

Specialized requirements for geothermal installations.

System Flushing and Valve Operation

Procedure for system cleaning and valve operation.

System Checkout and Installation Considerations

Pre-Energization System Checks

Essential checks before energizing the unit.

Electrical Installation Guidelines

Guidelines for voltage, wiring gauge, and grounding.

Wiring Gauge and Additional Devices

Thermostat wiring gauge and device addition cautions.

Unit Control Panel and Modes of Operation

Control Panel Features and Sensors

Description of control panel features and unit sensors.

Modes of Operation Overview

Overview of available operating modes.

Off, Heating, and Cooling Modes

Detailed operation for Off, Heating, and Cooling modes.

Unit Protection and Control Logic

Auto Changeover Mode Logic

Logic and operation of the auto changeover mode.

Unit Protection and Fault Handling

Protection against faults and intelligent reset.

Brownout Protection and Manual Lockout

Protection against brownouts and manual lockout reset.

Lead-Lag Compressor Operation

Explanation of lead-lag functionality for dual compressors.

Pump Cycling and Operating Instructions

Pump Cycling Functionality

How the optional pump relay cycles pumps with the compressor.

User Interface and Button Functions

Description of the control panel interface and buttons.

LED Indicators and Freeze Stat Note

Explanation of LED indicators and freeze stat bypass.

User Adjustable Settings and Controller Setup

User Adjustable Settings Chart

Table of adjustable settings, ranges, and defaults.

Controller Startup and Initial Settings

Process of controller startup and initial setting adjustment.

Set Point and Differential Examples

Examples illustrating set point and differential calculations.

Initial Configuration Steps

Temperature Scale and Pump Operation

Configuration of temperature scale and pump operation mode.

Dead Band and Auto Changeover Set Point

Setting the dead band and auto changeover set point.

Test Mode, Compressor, Lead Lag, Malfunction Settings

Configuration of test mode, compressor, lead lag, and malfunction.

Troubleshooting - General Unit Issues

Unit Troubleshooting - No Power/Fuse

Troubleshooting steps for units not running due to power or fuse issues.

Unit Troubleshooting - High Pressure

Troubleshooting causes for high pressure lockouts.

Unit Troubleshooting - Low Pressure

Troubleshooting causes for low pressure lockouts.

Unit Troubleshooting - Short Cycles

Troubleshooting causes for units short cycling.

Troubleshooting - Cooling/Heating and Comfort Alert

Unit Troubleshooting - Insufficient Output

Troubleshooting insufficient cooling or heating output.

Comfort Alert Module Flash Codes

Troubleshooting using Comfort Alert Module flash codes.

Comfort Alert Module Flash Codes

Flash Codes 5-7

Interpretation of Comfort Alert Module flash codes 5 through 7.

Flash Codes 8-9

Interpretation of Comfort Alert Module flash codes 8 through 9.

Troubleshooting - HRP, Lockouts, and LED Indications

HRP Troubleshooting

Troubleshooting specific issues with the Heat Recovery Package.

Unit Lockouts and Causes

Understanding and addressing unit lockouts.

UPM I and UPM II Board LED Indications

Interpreting LED status indications on UPM boards.

Electrical Data Table WW

WW Model Electrical Specifications

Table detailing electrical data for WW models.

Electrical Data Table WT

WT Model Electrical Specifications

Table detailing electrical data for WT models.

Water Pressure Drop WW

WW Model Pressure Drop Data

Table showing water pressure drop for WW models.

Water Pressure Drop WT

WT Model Pressure Drop Data

Table showing water pressure drop for WT models.

Water Quality Table

Acceptable Water Quality Values

Table listing acceptable water quality parameters for copper/cupro-nickel.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Wiring Diagrams - Components and Notes

Standard Components Legend

Legend for standard components in wiring diagrams.

Optional Components Legend

Legend for optional components in wiring diagrams.

Wiring Diagram Notes

Important notes and cautions for wiring diagrams.

Dimensional Drawings WW

WW Model Dimensions and Connections

Detailed dimensions and connection points for WW models.

Dimensional Drawings WT

WT Model Dimensions and Connections

Detailed dimensions and connection points for WT models.

Unit Start-Up, Maintenance, and Decommissioning

Unit Start-Up Procedure

Step-by-step guide for starting up the unit.

Maintenance and Decommissioning Information

Requirements for annual maintenance and decommissioning.

Environmental Protection and Recycling

Information on protecting the environment and recycling components.

Terminology

Glossary of Technical Terms

Definitions of technical terms used in the manual.

Unit Check-Out Sheet

Customer and Unit Nameplate Data

Fields for recording customer and unit identification data.

Operating Conditions Recording

Fields for recording operating conditions in cooling and heating modes.

Notes

General Notes Section

Blank section for user notes or additional information.

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Bosch WT Series User Manual

Table of Contents

Questions and Answers:

Bosch WT Series Specifications

Summary

Key to Symbols and Safety Warnings

Warnings and Important Information

Safety Warnings and Precautions

Refrigerant Handling Notice

Construction Use Prohibition

Model Nomenclature

WT Model Nomenclature

WW Model Nomenclature

Standard WW/WT Package Overview

General Description and Certifications

Moving, Storage, and Inspection

Location and Piping Requirements

Installation Guidelines

Electrical and Piping Considerations

Water Piping Recommendations

Electrical Safety and Wiring

Voltage and Circuit Protection

UPM Control and Safety Devices

UPM I and UPM II Controller Diagrams

Thermostat Malfunction Light Connections

Safety Controls and UPM Operation

Pressure Switches and Freeze Protection

UPM Board Settings and Features

UPM Timers and Protection Functions

Malfunction Output and 24VAC Wiring

UPM Functions and Options

Display Output and Test Mode

Freeze Sensor and Lockout Reset

Heat Recovery Package (HRP) Introduction

Heat Recovery Package (HRP) Details

HRP Freezing Precautions and Flow Proving

Pump Relay and Comfort Alert Module

HRP Water Tank Preparation and Piping

HRP Water Tank Refill Procedure

Sequence of Operation

Initial Start-Up Procedure

Cooling Mode Operation

Heating Mode Operation

Sequence of Operation Flow

Operational Flow Diagram

Application Considerations

Well Water Systems

Cooling Tower/Boiler Systems

Application Considerations

Air Elimination and Piping Notes

Geothermal Systems

System Flushing and Valve Operation

System Checkout and Installation Considerations

Pre-Energization System Checks

Electrical Installation Guidelines

Wiring Gauge and Additional Devices

Unit Control Panel and Modes of Operation

Control Panel Features and Sensors

Modes of Operation Overview

Off, Heating, and Cooling Modes

Unit Protection and Control Logic

Auto Changeover Mode Logic

Unit Protection and Fault Handling

Brownout Protection and Manual Lockout

Lead-Lag Compressor Operation

Pump Cycling and Operating Instructions

Pump Cycling Functionality

User Interface and Button Functions

LED Indicators and Freeze Stat Note

User Adjustable Settings and Controller Setup

User Adjustable Settings Chart

Controller Startup and Initial Settings

Set Point and Differential Examples

Initial Configuration Steps

Temperature Scale and Pump Operation

Dead Band and Auto Changeover Set Point

Test Mode, Compressor, Lead Lag, Malfunction Settings

Troubleshooting - General Unit Issues

Unit Troubleshooting - No Power/Fuse

Unit Troubleshooting - High Pressure