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60
60
120 volts
present?
* Loose
connection at
fan plug or fan
capacitor
* Defective
capacitor
* Defective fan
24 volts present
across yellow
transformer lead and
purple lead on
pressure switch?
*Defective "FAN"
relay
*Defective CB502
board
Continued
from previous
page
Unplug fan and
check for 120V
across H FAN
and N FAN on
CB502 board
*Loose pressure
switch harness
*Defective CB502
board
PRESS
LED on?
FAN
LED on?
LIMIT
LED on?
Fan On?
24V between
brown lead on
limit and yellow
lead on
transformer?
* Boiler water
temp over L4080D
setpoint
*Defective L4080D
* Missing or loose
"RESET CONTROL"
jumper
*Missing or loose
"CN1" jumper
*Defective CB502
board
N
Y
N
N
* Kinked or blocked
vacuum switch tubing
* Defective vacuum
switch
N
Y
Y
N
24 volts present
across yellow
transformer lead and
red lead on pressure
switch?
N
Y
Minimum
pressure at
switch called in
Table 7 present
across switch?
*Tubes reversed on
pressure switch
*Leak in tubes at pressure
switch connection
*Loose pressure switch
harness connection
*Defective CB502 board
Y
N
N
YYY
N
Y
TROUBLESHOOTING CHART FOR BOILERS WITH CB502 CONTROL SYSTEM (USING #42-502A BOARD)
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