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APEX Installation, Operating, & Service Instructions APEX Installation, Operating, & Service Instructions
Table 12-8: Sensor Fault Diagnostic Help
Indication Possible Cause
Not Installed
Sensor has not been selected. For example, in Figure 12-7, the Header Sensor has not been
selected. Refer to Operations Section, Parameter Adjustment for information on how to select
sensors.
Open Sensor not connected or loose wire. Check sensor wiring.
Shorted
Sensor terminals connected to each other or sensor has failed.
• Check sensor wiring.
• Check sensor resistance. See Tables 12-9 through 12-12 for temperature versus resistance
values.
Outside low range
Outside high range
Sensor input out of range. Sensor is defective or is being subjected to electrical noise.
Not reliable Sensor is defective or is being subjected to electrical noise.
Table 12-9: Supply and Flue Sensor
Temperature vs. Resistance,
10kOhm NTC, Beta = 3977K
Table 12-10: Return Sensor
Temperature vs. Resistance,
12kOhm NTC, Beta = 3750K
Temperature Ohms of
Resistance
°F °C
32 0 36100
50 10 22790
68 20 14770
77 25 12000
86 30 9810
104 40 6653
122 50 4610
140 60 3250
158 70 2340
176 80 1710
194 90 1270
212 100 950
230 110 730
248 120 560
Temperature Ohms of
Resistance
°F °C
32 0 32650
41 5 25390
50 10 19900
59 15 15710
68 20 12490
77 25 10000
86 30 8057
95 35 6531
104 40 5327
113 45 4369
122 50 3603
131 55 2986
140 60 2488
149 65 2083
158 70 1752
167 75 1481
176 80 1258
185 85 1072
194 90 918
203 95 789
212 100 680
12 Troubleshooting (continued)
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