A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000©
Training Department
24
TROUBLESHOOTING
STEP 8 - TEMPERATURE THERMISTOR CHECK
STEP 8. TEMPERATURE THERMISTOR CHECK.
The ohm’s resistance thru a thermistor is interpreted by the control board as a water temperature reading.
• Note tank water temperature on display board or tank a thermometer reading from the T&P valve and
drain valve
• Disconnect plugs from CN 3 and CN 8
• Set multimeter to read “resistance” (20 K scale)
Check the ohm’s resistance from black to black on the CN 3 plug and black to black on the CN 8 plug.
IF… THEN
Ohm reading does not (approximately) correspond
to table information
Ohm reading does correspond (approximately) to
the table information.
replace
o to St
Note: Thermistors are very reliable unless a wire is cut or
connection loose. A "bad" thermistor temperature sensor is
unlikely to be the problem.
°C °F
3 40 26,435
21 70 11,974
37.5 100 5,862
49 120 3,780
54.5 130 3,066
60 140 2,503
71 160 1,698
82 180 1,177
Water Temp OHMS
Resistance
Upper Temperature Probe Plug
Lower Temperature Probe Plug
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