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59
N
Y
Y
Call for heat
from
"DHW/H2"
zone
"DHW/H2"
circulator
start?
Defective
CB502 board
DHW
LED On?
24V across
"DHW/H2" T
and T
* Loose connection in
t'stat or zone valve end
switch wiring
* Defective t'stat or zone
valve end switch
* T'stat or zone system
miswired-consult zone
valve or t'stat
manufacturer's
instructions.
N
120 volts across
blue and white
circulator leads?
*Loose
connection
between boiler
J-box and circ
* Defective "DHW/H2"
relay on CB502
* Relay not fully seated
in socket
* Loose connection in
circulator wiring
Y
N
N
Continued on
next page
Y
TROUBLESHOOTING CHART FOR BOILERS WITH CB502 CONTROL SYSTEM (USING #42-502A BOARD)
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