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Introduction
The 120T Ultra High Efficiency Water Heater is designed to deliver a high thermal efficiency rating, in
a quiet running unit with venting options that allow for installation flexibility. Several technologically
advanced design features are incorporated in the design that will require additional knowledge on the
part of the qualified service provider. The information in this manual will instruct service and
maintenance professionals on the function, proper diagnosis, and repair of this water heater.
The 120T Ultra High Efficiency Water Heater uses a low NOx premix power burner located at the top
of the water heater to direct a turbulent flame down into a submerged combustion chamber. The
turbulence causes a thorough mixing of gas and air for optimum combustion. The combustion gases
then travel through a three pass flue system, keeping the gases moving at a high velocity. The
combination of high turbulence and velocity results in an optimum transfer of heat from the flue gases
into the water.
Burner operation is controlled using an electronic ignition control board. The control board monitors the
status of the electronic thermostat, vent temperature limit switch, vent system pressure switch, a flame
sensor, spark rod, and gas valve. The control board contains programming which determines the
sequence of operation and timings for purge periods, trial for ignition, flame sensing, and lockouts. The
control board modulates the water heater to adjust the firing rate to account for varying hot water
demands. Additionally, the control board will provide diagnostic information both on the control board
and digital display to help in determining the cause of system lockouts.
The contents in this manual are detailed informational tools to assist in the proper diagnosis of the 120T
Ultra High Efficiency Water Heater operational faults. Please read the entire Service Manual, which
provides detailed information regarding the 120T Ultra High Efficiency Water Heater operation and
installation specific concerns.
How To Use This Manual
It is intended for this manual to be used by qualified service personnel for troubleshooting analysis and
repair of the 120T400/500 models. Understanding the sequence of operation section of this manual will
contribute greatly to troubleshooting this product.
An Installation Checklist is shown on page 44. Compare the installation against this installation checklist
to confirm all requirements are met.
A Service Report is shown on page 45. Completing this form will assist in the troubleshooting efforts.
Should you need to call for technical support, please provide the information shown on this form to the
support technician to ensure accurate troubleshooting.
Troubleshooting begins with System Observation to determine failure mode as indicated by error codes
on the system display. Troubleshooting continues with Failure Modes and Probable Cause, directing
the service provider to a series of test procedures to determine the root cause of failure. Component
replacement procedures directly follow the test procedures for a given component.
In some difficult to diagnose conditions, it may be necessary to isolate the heater from the vent system
to determine root cause.
Contact Technical Support immediately if diagnosis is not determined using the methods described in
this service manual.
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Summary of Contents for EF120T4003N3
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