Checking Temperature Sensors - Crest Audio FBN0751 Service Manual

3
Troubleshooting

Checking temperature sensors

The boiler temperature sensors (inlet water, outlet water, system water, flue, and outdoor air) are all resistance type devices. The
following tables show the correct values for the sensors at various temperatures. Use an ohmmeter to read the resistance of the
sensor at a known temperature. If the resistance of the sensor does not closely match its corresponding table, replace the sensor
It is important to note that the flue, inlet air (pre-mix), and outlet water sensors each have two temperature sensing devices in
one housing. These devices are designated as S1/S9 - outlet sensor, S3/S1 - flue sensor, and S11/S13 - inlet air (pre-mix) sensor.
Please reference the wiring diagram in the Crest Installation and Operation Manual for correct terminal location.
Table 3B - Inlet Water/System Sensor Resistance vs.
Temperature
Temperature Resistance Temperature Resistance
50 18,780
68 12,263
86 8,194
104 5,592
122 3,893
140 2,760
Table 3D - Outlet Water Sensor Resistance vs. Temperature
Outlet S1
Pre-Mix Air S11
Temperature Resistance Temperature Resistance Temperature Resistance Temperature Resistance
50 19,553
68 12,690
86 8,406
104 5,715
122 3,958
140 2,786
Table 3E - Flue Sensor Resistance vs. Temperature
Flue S3
Temperature Resistance Temperature Resistance Temperature Resistance Temperature Resistance
50 40,030
68 25,030
86 16,090
104 10,610
122 7,166
140 4,943
(continued)
158 1,990
176 1,458
194 1,084
212 817
R/Y
GY/Y
158 2,004
176 1,464
194 1,084
212 816
GY/Y
158 3,478
176 2,492
194 1,816
212 1,344
Table 3C - Outdoor Air Sensor Resistance vs. Temperature
Temperature Resistance Temperature Resistance
-50 490,813
-40 336,606
-30 234,196
-20 165,180
10 118,018
0 85,362
10 62,465
Outlet S9
50 40,030
68 25,030
86 16,090
104 10,610
122 7,166
140 4,943
Flue S10
50 258,500
68 125,500
86 80,220
104 52,590
122 35,270
140 24,160
Service Manual
20 46,218
30 34,558
40 26,099
50 19,900
60 15,311
70 11,883
80 9,299
RW/Y
158 3,478
176 2,492
194 1,816
212 1,344
W/Y
158 16,870
176 12,000
194 8,674
212 6,369
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