3
Troubleshooting
30
Service Manual
Table 3B -
Inlet/Outlet System Sensor Resistance vs. Temperature
Temperature
Resistance
Temperature
Resistance
50
18,780
158
1,990
68
12,263
176
1,458
86
8,194
194
1,084
104
5,592
212
817
122
3,893
140
2,760
Table 3C -
Flue Temperature Sensor Resistance vs. Temperature
Temperature
Resistance
Temperature
Resistance
68
14,773
176
1,707
86
9,804
194
1,266
104
6,652
212
952
122
4,607
230
726
140
3,252
248
560
158
2,337
Table 3D -
Outdoor Air Sensor Resistance vs. Temperature
Temperature
Resistance
Temperature
Resistance
-50
490,813
20
46,218
-40
336,606
30
34,558
-30
234,196
40
26,099
-20
165,180
50
19,900
10
118,018
60
15,311
0
85,362
70
11,883
10
62,465
80
9,299
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.
