Checking Temperature Sensors - Lochinvar Armor 100 Series Service Manual

3
Troubleshooting

Checking temperature sensors

The water heater temperature sensors (inlet water, outlet water, system water, and flue) 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 have two temperature sensing devices in one housing. These devices
are designated as S1a/S1b, outlet sensor and S3a/S3b, flue sensor. Please reference the wiring diagram in the Armor Water Heater
Installation and Operation Manual for correct terminal location.
Table 3B - Inlet System Sensor Resistance vs. Temperature
Temperature °F
50
68
86
104
122
140
Table 3C - Outlet Water Sensor Resistance vs. Temperature
(Wire Color - R/BK and Y)
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 3D - Flue Sensor Resistance vs. Temperature
(Wire Color - W/B and Y)
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
30
(continued)
Resistance 
18,780
12,263
8,194
5,592
3,893
2,760
S1a
158 2,004
176 1,464
194 1,084
212 816
S3a
158 3,478
176 2,492
194 1,816
212 1,344
Service Manual
Temperature °F
158
176
194
212
--
--
S1b
(Wire Color - G and Y)
50 40,030
68 25,030
86 16,090
104 10,610
122 7,166
140 4,943
S3b
(Wire Color - PR and Y)
50 258,500
68 125,500
86 80,220
104 52,590
122 35,270
140 24,160
Resistance 
1,990
1,458
1,084
817
--
--
158 3,478
176 2,492
194 1,816
212 1,344
158 16,870
176 12,000
194 8,674
212 6,369