Resettable Thermal Switch Testing And Replacement - Bradford White MI30T*F(BN,CX,SX) Service Manual

National Excelsior Company
www.excelsiorhvac.com
The Bradford White
DEFENDER
Safety System
RESETTABLE THERMAL SWITCH CONTINUITY TESTING
Step 1. Remove outer jacket door.
Step 2. Disconnect wire leads from resettable thermal switch.
Step 3. Using a multimeter capable of measuring continuity (Ohms),
place one probe of meter on one of the brass connection tabs of
the resettable thermal switch, and the remaining probe on the
other connection tab.
Step 4. If continuity is indicated, the switch is closed, allowing millivolt current to pass.
Step 5. If continuity is not indicated, the switch is open, possibly due to an over heating condition. The switch is
designed to open at predetermined temperatures depending on model. An open switch can be reset by
depressing the red colored button located at the center of the switch. The overheating condition must be
determined prior to putting the heater back in service.
PROBABLE CAUSE FOR RESETTABLE THERMAL SWITCH ACTIVATION
PROBABLE CAUSE
Insufficient combustion air
1. Weak switch or switch
out of calibration.
2. Incorrect switch.
Flammable vapor incident
34 34
®
CORRECTIVE ACTION
1. Verify adequate combustion air supply is
available.
2. Clear jacket slot openings of any dirt, dust,
restrictions or other obstructions.
3. inspect flame arrestor plate and clean with
stiff brush and/or vacuum to remove scale
deposits and debris.
1. Replace resettable thermal switch
2. Verify switch color code and approximate
temperature.
1. Replace water heater.
34
Subject to change without notice.
SERVICE PROCEDURE RG-VIII
Resettable Thermal Switch
Testing and Replacement
Resettable thermal switch
color code reference.
Approximate switch
Color Code activation temperature
Blue
Yellow
Red
(open)
240°
270°
290°