S U F S E R V I C E H A N D B O O K
T R O U B L E S H O O T I N G
TEMPERATURE PROBE
STEP 6
TEMPERATURE PROBE RESISTANCE
UPPER | LOWER |
TEMPERATURE | TEMPERATURE |
PROBE PLUG | 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… | THEN | |
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ohm reading does not approximately correspond to table at given | replace temperature probe if thermistor is open. | |
temperatures | shorted, or resistance value is off significantly. | |
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ohm reading does approximately correspond to table at given | continue to Step 7. | |
temperatures | ||
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WATER TEMP | OHMS RESISTANCE | ||
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°C | °F | ||
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3 | 40 | 26,435 | |
21 | 70 | 11,974 | |
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37.5 | 100 | 5,862 | |
49 | 120 | 3,780 | |
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54.5 | 130 | 3,066 | |
60 | 140 | 2,503 | |
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71 | 160 | 1,698 | |
82 | 180 | 1,177 | |
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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.
State Water Heaters | 23 | Technical Training Department |
Ashland City, Tennessee © 2004 |
