Temperature Probe - State Water Heaters Utra-Force STC-077 Service Handbook

STEP 6 TEMPERATURE PROBE RESISTANCE
UPPER
TEMPERATURE
PROBE PLUG
STEP 6: CHECK RESISTANCE OF THERMISTOR IN UPPER AND LOWER TEMPERATURE
PROBES.
Condition:
• Disconnect CN3 and CN8 plugs from control board.
• On/Off switch is off.
• Multimeter is set to lowest ohms scale above expected resistance.
Check resistance between black wire connects on CN3 and CN8 plugs as shown in illustration
above.
IF...
ohm reading does not approximately correspond to table at given
temperatures
ohm reading does approximately correspond to table at given
temperatures
WATER TEMP
°C °F
3 40
21 70
37.5 100
49 120
54.5 130
60 140
71 160
82 180
State Water Heaters
Ashland City, Tennessee © 2004
S U F S E R V I C E
T R O U B L E S H O O T I N G

TEMPERATURE PROBE

OHMS RESISTANCE
26,435
11,974
5,862
3,780
3,066
2,503
1,698
1,177
H A N D B O O K
LOWER
TEMPERATURE
PROBE PLUG
THEN
replace temperature probe if thermistor is open.
shorted, or resistance value is off significantly.
continue to Step 7.
NOTE: The upper and lower temperature probes contain
thermistors which are heat sensitive resistors. The control
board interprets changes in thermistor resistance as
changes in water temperature.
These thermistors are very reliable and should only be
replaced when:
The resistance test indicates an "open" (infinite resistance)
or a "direct short" (no resistance) circuit.
The nature of the service problem is temperature control
and the resistance readings are significantly off when com-
pared to the values in the table here at the given tempera-
ture.
23
Technical Training Department
STC-077