Bradford White UCG100H399, Service Manual

Page: 17 / 48

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T he r m o s tat C ir cu i t T est i ng and Rep l acement
I MPOR T AN T NO T E: T his procedure assumes a coo l tank .
1 2 0 vo l t potentia l exposure . Use caution making
vo l tage checks to avoid persona l injury .
WARN I NG
Use caution not to damage connectors when
making vo l tage measurements or jumping
termina l s
CAU TI ON
C o nd i t io n: Wate r heate r n o t o pe r at i ng .
D i sp l ay sh o ws e rror c o de “93” (sens or
r ead i ng fau l ty)
N
Unp l ug or disconnect e l ectrica l power to the water heater .
Check continuity of wire harness to sensor . Resistance of
harness shou l d be c l ose to 0 ohms . Rep l ace wire harness
if high resistance is measured (over . 5 ohms) . Check
wires for intermittent connections, shorts, frayed
insu l ation . Rep l ace if necessary .
I f wire harness is O . K . , check sensor resistance detai l ed
in “Appendix – A : sensor resistance at various
temperatures” at the end of the thermostat testing and
rep l acement section . Rep l ace sensor if needed .
Turn power O N to water heater . Run water heater through
heating cyc l e and verify proper operation . Sensor
temperature can be viewed when burner shuts off (see
section on viewing the disp l ay in “Service Mode”) .
C o nd i t io n: Wate r heate r n o t o pe r at i ng . D i sp l ay
sh o ws e rror c o de “80” h i gh wate r tempe r atu r e
( o ve r 200 ° F) .
WARN I NG
D o n o t r eset the d i sp l ay f ro m the ha r d lo ck o ut
state w i th o ut c orr ect i ng the cause o f the
o ve r heat i ng c o nd i t io n .
Turn power O FF. Draw water to coo l tank be l ow 1 2 0 ° F
Check sensor . Sensor is he l d in p l ace with a c l ip fastened
to the we ll (see photo) . Check sensor wire for potentia l
damage or breaks in the wire insu l ation . I s the sensor fu ll y
inserted into the we ll?
I f sensor c l ip is damaged rep l ace
c l ip . Rep l ace sensor if damaged .
Check sensor resistance (see Sensor
Resistance Testing, fo ll owing section) .
Continued on
next page .
Y
Checking
continuity of
sensor
(disconnected
from contro l board .
Sensor shown fu ll y
inserted into we ll
Sensor c l ip shown
proper l y insta ll ed
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