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