Safety Circuit Voltage Trace - Bradford White M1TW40S Series Service Manual

Safety Circuit Voltage
Trace
NOTE: This procedure assumes a cool tank.
Remove three screws (Phillips Screw driver) from control access
cover on blower and remove cover (see photo 26).
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)
Y
Is there 10 to 13 VAC between yellow
wire leading from pressure switch and
green ground wire?
(see photo 27)
Y
Do you hear or can you
see the igniter sparking?
Y
Safety circuit
voltage is OK.
If burner does not light,
observe LED flash code
on gas valve and refer to
troubleshooting section
on page 13
making voltage checks to avoid personal injury.
Is LED on gas valve flashing
N
the "heartbeat" code
(alternating bright/dim)
N
Verify 115VAC to gas
control (see page 30)
N
Correct igniter/
sensor problem.
Check igniter/sensor
N
(see page 17)
is igniter/sensor OK?
27
TTW SERVICE PROCEDURE VIII

Safety Circuit Voltage Trace

WARNING
115 volt potential exposure. Use caution
Y No voltage from gas control,
call for technical support.
Is there continuity
through blower
temperature switch?
(see page 22)
N
Determine cause of blower
temperature switch
activation and correct.
Faulty cord set or
Y
gas control.
26
Check for loose or
broken wire
Y
connection at switch
terminals
Green ground wire
Red wire leading to
blower temp. switch
Yellow wire
leading from
pressure switch
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