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Technical Service Bulletin
12 kW Electric Tankless Water Heater
Troubleshooting Guide
Models: AE12, RP12T, US12
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.
Installation #1 (front view)
Installation #1 (front view)
Hot
Hot
Cold
Cold
Installation #2 (front view)
Installation #2 (front view)
Hot
Hot
Cold
Cold
Figure 1
Hot
Hot
Cold
Cold
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Related Manuals for Bosch US12
Summarization of Contents
Introduction
Who should perform the troubleshooting?
Identifies qualifications needed to perform troubleshooting safely with 240VAC.
What does this troubleshooting guide cover?
Explains the scope and purpose of the troubleshooting guide for diagnosing water heater issues.
Step 2 - Water supply and water heater settings
Check temperature knob setting
Ensures the temperature spindle is set all the way clockwise for proper operation.
Verify flow rate
Measures water flow in gallons per minute (GPM) to ensure proper heater activation.
Checking for plumbing crossovers
Tests for crossover issues, like a mixing valve leak, affecting hot water supply.
Step 3 - Physical inspection
Visual Inspection
Inspects internal components for burn marks, damaged wires, or misaligned parts.
Step 4 - Checking continuity and resistance
Check the flow switch for continuity
Tests the flow switch with and without water to check for proper function.
Check for continuity between connections labeled A-B and also C-D
Tests continuity of specific connections on the circuit board for troubleshooting.
Step 5 - Verify the power supply
Check to see if either element is grounded to the water tubing
Tests for ground faults by checking resistance between elements and water tubing.
Measure the incoming voltage across L1 and L2 terminals
Verifies the unit is receiving the correct 240 VAC power supply.
Need help?
Do you have a question about the US12 and is the answer not in the manual?
Questions and answers