Bradford White U-TW4-75S-76R-3N - Manual (Page 31)

U TTW SERVICE PROCEDURE X
Safety Circuit Voltage Trace
Safety Circuit Voltage Trace
WARNING
115 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 26).
Red wire leading to
blower temp. switch
Green ground wire
26
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 26)?
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 115VAC to gas
control (see page 32).
Is there continuity
through blower
temperature switch
(see page 24)?
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 19).
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
Page 31
25
Step 1. Remove three screws (Phillips
Screw driver) from control
access cover on blower and
remove cover (see photo 24
and 25).
Faulty cord set or
gas control.
Y
Correct igniter/
sensor problem.
Control Access
Cover Screws
24
R
31