Bradford White U-TW4-75S-76R-3N - Manual (Page 24)

U TTW SERVICE PROCEDURE VI
Blower Temperature Switch Testing
and Replacement
Blower Temperature Switch
Testing. WARNING
115 volt potential exposure. Use caution
to avoid personal injury.
18
Disconnect wire leads to
switch. Using a multi-meter
set to the ohms setting, is
there continuity between the
switch terminals?
Switch OK
Cool switch to
below 130°F
N
Y
Switch Setting
Opens on rise @ approximately 165°F
Auto resets on fall @ approximately 130°F
Step 1. Position gas control power switch
to the “OFF” position.
Step 2. Remove the three screws (Phillips
screw driver) from control access
cover on blower and remove cover
(see photos 17 and 18).
Step 3. Locate blower temperature switch
(see photo 19).
Reconnect wire leads and
observe heater operation. Do
exhaust gas temperatures rise
to or above 165°F?
Replace switch
(see page 25).
Y
N
Do switch contacts
open?
Do switch contacts
open?
N
Y
Replace switch
(see page 25).
N
Y
Exhaust
temperature is too
hot.
Common causes for
high exhaust temperature
1. Vent length is below minimum allowable.
2. Vent diameter not to specification.
3. Restricted dilution air inlet.
4. Missing or deteriorated flue baffle.
5. Gas pressure is out of specification.
Blower temperature
switch location
19
Air mixing inlet
Page 24
Gas Control shown in the “OFF” position
Control Access
Cover Screws
17
R
24