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58
58
120 volts across
black and white
transformer
primary leads ?
Call from
"HEAT 1"
zone
"HEAT 1"
Circulator
start?
* Power off
* Blown fuse or
tripped breaker
* Miswired or
loose electrical
connection in
120 volt line
120 volts
across red and
white circulator
leads?
* 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
Y
N
N
Y
N
Y
N
START
(No call for
heat from
either zone)
Y
Y
24volts
transformer
secondary?
* Defective
transformer.
* Loose
connection
between boiler
J-box circ.
* Defective
circulator
* Defective "HEAT 1" relay
on CB502
* Relay not fully seated in
socket
Y
Y
N
Y
N
Y
PWR
LED On?
HEAT
LED On?
"DHW
PRIORITY"
Switch on?
*Defective
transformer
harness
*Defective
CB502
24V across
"HEAT 1" T
and T
"DHW/H2"
zone used?
*Defective CB502
board
*Defective
"DHW/H2" relay
*Defective CB502
board
N
Y
N
TROUBLESHOOTING CHART FOR BOILERS WITH CB502 CONTROL SYSTEM (USING #42-502A BOARD)
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