Bosch AE12 User Manual

12 kW Electric Tankless Water Heater
Troubleshooting Guide
Models: AE12, RP12T, US12
Technical Service Bulletin
DANGER: ELECTRIC SHOCK
 ELECTRICITY IS EXTREMELY DANGEROUS.
TAKE EXTRA PRECAUTIONS AND
DISCONNECT THIS PRODUCT FROM THE
ELECTRICAL SUPPLY BEFORE CLEANING,
SERVICING OR REMOVING THE COVER.
 BOSCH ELECTRICAL APPLIANCES
SHOULD ONLY BE SERVICED BY A TRAINED
TECHNICIAN OR LICENSED ELECTRICIAN.
Bosch technical support is available at 866-330-2729.
Please document results from each troubleshooting step
prior to calling. Without this information documented, we
cannot make a determination as to what is wrong with your
water heater. This will delay a resolution.
Introduction
Who should perform the troubleshooting?
Anyone who has the qualifications to work safely with 240VAC. If you
do not possess the tools or the knowledge to work safely with
240VAC, contact a licensed professional.
What does this troubleshooting guide cover?
This guide covers every test we can advise you to perform on the
location, installation, and water heater. With ALL the information
from ALL the tests in this guide, it is possible to diagnose any water
heater of this type to a point where we can advise a repair or cover
warranty.
Required tools:
 Adjustable wrench
 Empty gallon container
 Digital multi-meter
 Phillips head screwdriver
 Flat head screwdriver
Step 1 – Document installation details
 Record information in Step 1 of the Building and Install
questionnaire on page 5.
DANGER: ELECTRIC SHOCK
 FOR STEPS 2, 3 AND 4,
SHUT OFF THE
CIRCUIT BREAKER POWERING THE
APPLIANCE, LOCK IT, AND VERIFY THAT
THERE IS NO VOLTAGE AT THE UNIT.
Step 2 – Water supply and water heater settings
 Verify the heater is installed in one of the two positions (inlet/
outlet connection on bottom) shown in Fig. 1.
Hot
Cold
Hot
Cold
Hot
Cold
Installation #1 (front view)
Installation #2 (front view)
H
ot
C
old
H
o
t
C
old
Ho
t
C
old
I
nstallation
#
1
(f
ront view
)
I
nstallation
#
2
(f
ront view
)
Figure 1

Bosch AE12 Specifications

General

Brand	Bosch
Model	AE12
Category	Water Heater
Language	English

Summary

Introduction to Troubleshooting

Who Should Perform Troubleshooting

Identifies qualifications needed to safely work with 240VAC appliances.

Scope of the Troubleshooting Guide

Details what tests the guide covers for diagnosing water heater issues.

Step 1: Document Installation Details

Record Questionnaire Information

Instructs to record details from the Building and Install questionnaire.

Step 2: Water Supply and Heater Settings

Verify Cold Water Supply Connection

Ensures the cold water supply is correctly connected to the unit's INLET.

Check Temperature Knob Setting

Procedure to check and set the temperature control knob.

Plumbing Crossover Test Procedure

Details steps to identify and correct plumbing crossovers impacting performance.

Step 3: Physical Inspection

Inspect Internal Components

Visual inspection for burn marks, damaged wires, or component alignment.

Checking the Thermal Cut Out

Locate and Reset Thermal Cut Out

Instructions on how to find and reset the thermal cut out switch.

Thermal Cut Out Trip Causes

Notice explaining common reasons for the thermal cut out tripping.

Step 4: Continuity and Resistance Checks

Check Flow Switch Continuity

Tests continuity of the flow switch with and without water flow.

Check Thermal Cut Out Continuity

Tests continuity of the thermal cut out switch terminals A-B and C-D.

Element Resistance and Grounding

Measure Element Resistance

Procedure to measure resistance of heating elements using a multimeter.

Check Elements for Grounding

Tests if heating elements are grounded to the water tubing.

Step 5: Verify Power Supply

Measure Incoming Voltage

Verifies the unit is receiving 240 VAC by measuring voltage at L1 and L2.

Questionnaires

Building and Installation Questionnaire

Form for recording installation details and water supply information.

Water Heater Troubleshooting Questionnaire

Form for documenting results of troubleshooting steps and component checks.