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E. Thermistor Check
If the error code “H1” “H2” “H3” or “H4” or an abnormal temperature [above 231°F (111°
C) or below -6°F (-21°C)
] appears in the display, or the wash tank water boils, check the
thermistor(s) according to the procedure below. If replacement is required, see “IV.M.
Removal and Replacement of Thermistor.”
1) Move the power switch (GFCI) to the “OFF” position, then turn off the power supply.
Lockout/Tagout to prevent the power from being turned back on inadvertently.
2) Remove the control box cover, then disconnect the CN7 connector from the control board
(see “II.D.2. Control Board Layout”).
3) To check the wash tank thermistor, check the resistance across the brown wires (#1 and
#2). To check the internal booster tank thermistor, check the resistance across the purple
wires (#3 and #4). See the table below for proper resistance and temperature relations.
Temperature [°F (°C)]
Resistance [kΩ]
194 (90)
4.30 to 4.62
176 (80)
5.87 to 6.38
158 (70)
8.13 to 8.96
140 (60)
11.5 to 12.8
104 (40)
24.3 to 28.0
68 (20)
56.3 to 67.1
32 (0)
145.6 to 180.6
4) If any problem is found, replace the thermistor according to “IV.M. Removal and Replacement
of Thermistor.”