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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 and outlet water sensors each have two temperature sensing devices in one housing. These
devices are designated as S1/S9 - outlet sensor and S3/S10 - flue 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 & Pre-Mix Air 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
43
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