Weil-McLain GV90+, Manual

Page: 78 / 108

Part number 550-143-010/1021
78
GV90+
series
2
gas-fired water boiler – boiler manual
Return temperature sensor
1. See Figure 89.
2. Resistance check method:
a. With the boiler operating, use a contact thermometer to
measure the temperature of the return pipe next to the re-
turn temperature sensor. Make a note of the temperature.
b. Turn the boiler ON/OFF switch off.
c. Immediately disconnect the return temperature sensor
plug from the IBC.
d. Measure the resistance of the sensor. Write down the
result.
e. Let the sensor cool to room temperature and measure the
resistance again. Write down the result.
f. Compare the sensor resistances at both temperatures to
the closest temperatures in Figure 90.
Troubleshooting
(continued)
Supply Temperature/ LWCO sensor
1. See Figure 91.
2. The boiler temperature/LWCO sensor is a resistance-type
device.
3. The Table, shows the correct value for the sensor at various
temperatures.
4. Use the resistance values at 32°F, 60°F, 70°F and 212°F to
measure the sensor resistance at known temperatures (ice
point, room temperature and sea level boiling point). For ice
point and boiling point, insert the sensor in water at that tem-
perature. Use an ohmmeter to read resistance value between
thermistor # and thermistor common. See Figure 93, page 80 ,
for sensor plug details.
g. If the measured values are within 10% of the values listed,
the sensor is good. If not, replace the sensor. See Replace-
ment parts for the part number.
3. Fixed resistor method
a. With the boiler power OFF, disconnect the return tem-
perature sensor plug at the IBC.
b. Insert a 2500-ohm resistor into the IBC sensor plug.
c. Restart the boiler.
d. If the boiler operates with the resistor, but not with the
sensor, try replacing the sensor. See Replacement parts
section for the part number.
Figure 89
Return temperature sensor
Sensor resistance values
Temp
(°F)
Sensor ohms
Temp
(°F)
Sensor ohms
Min. Max Min. Max
32 34265 37871 120 4517 4992
40 27834 30764 130 3698 4088
50
21630 23907
140
3043 3364
60 16944 18727 150 2517 2782
70 13372 14780 160 2091 2311
80 10629 11747 170 1744 1928
90 8504 9399 180 1461 1615
100 6847 7568 190 1229 1359
110 5545 6129 200 1038 1147
Table sensor resistance values
Figure 90 Return temperature sensor resistance
Temperature
°F
Resistance
Ohms
Temperature
°F
Resistance
Ohms
60
15300
140
2480
70 11900 160 1680
80 9310 180 1160
100 5840 200 810
120 3760 212 674
Figure 91
Supply Temperature/LWCO sensor