Bradford White TW4-75S-76B-3X - Manual (Page 28)

TTW SERVICE PROCEDURE VIII
Safety Circuit Voltage Trace
Safety Circuit Voltage
Trace
WARNING
120 volt potential exposure. Use caution
making voltage checks to avoid personal injury.
Position gas control switch to the “ON”
position and adjust thermostat dial to call
for heat, Is there 10 to 13 VAC between
red wire leading to blower temperature
switch and green ground wire?
Blower must be running during this
voltage check.
(see photo 27)
Red wire leading to
blower temp. switch
Green ground wire
27
Yellow wire
leading from
pressure switch
Y
Is there 10 to 13 VAC between yellow
wire leading from pressure switch and
green ground wire?
(see photo 27)
Do you hear or can you
see the igniter sparking?
Y
Y
Is LED on gas valve flashing
the “heartbeat” code
(alternating bright/dim)
N
Safety circuit
voltage is OK.
No voltage from gas control,
call for technical support.
Y
NOTE: This procedure assumes a cool tank.
Verify 120VAC to gas
control (see page 29)
Is there continuity
through blower
temperature switch?
(see page 21)
Y
Check for loose or
broken wire
connection at switch
terminals
N
N
Determine cause of blower
temperature switch
activation and correct.
Check igniter/sensor
(see page 16)
is igniter/sensor OK?
If burner does not light,
observe LED flash code
on gas valve and refer to
troubleshooting section
on page 12
N
N
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26
Step 2. Remove three screws (Phillips Screw driver) from control
access cover on blower and remove cover (see photo 26).
Faulty cord set or
gas control.
Y
Correct igniter/
sensor problem.
28