Temperature - A.O. Smith BTH 120 Service And Parts Manual

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...
Ohm reading does not (approximately) correspond
to table information
Ohm reading does correspond (approximately) to
the table information.
Water Temp
°C °F
3 40
21 70
37.5 100
49 120
54.5 130
60 140
71 160
82 180
Upper Temperature Probe Plug
A. O. Smith Water Products Company
Irving, Texas 2000©
TROUBLESHOOTING
STEP 8 - TEMPERATURE THERMISTOR CHECK
OHMS
Resistance
Note: Thermistors are very reliable unless a wire is cut or
26,435
connection loose. A "bad" thermistor temperature sensor is
11,974
unlikely to be the problem.
5,862
3,780
3,066
2,503
1,698
1,177
THEN
replace
go to St
Lower Temperature Probe Plug
24
Service Handbook
Training Department