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Test 18.A: Faulty Sensor / Faulty Wire Harness Test
Test 18: Maxed out Sensor Readings
1. Open
Panel 2 (Touch screen should be off).
2. Find the analog input terminal strip shown in the picture below.
3. Make sure the multimeter is set to measure Ω (Ohms) / continuity.
4. Place one lead on the 24 V wire and the other lead on each of the 4-20mA wires one at a time; there
should not be continuity (you should see an “OL” Open Loop or very high ohms).
5. If there is a 4-20mA wire that has continuity with the 24 V wire, unplug the respective sensor.
6. Test the wire again with the sensor unplugged. If there is no continuity, this indicates a faulty sensor;
If there is still continuity, this indicates a faulty wire harness.
*If replacing the faulty sensor does not fix the problem, go to Test 13.
**If replacing the faulty sensor does not fix the problem and you have a good input card (Test 13), replace the
PLC.
Tests
1
5
6
3
4
2
1-Flue T
emp Sensor
Card 1
Card 2
Faulty
Sensor
Faulty Wire
Harness
4-20mA wires
24 V wire
2-Boiler W
at
er T
emp Sensor
3-F
eed W
at
er T
emp Sensor
4-Ambien
t T
emp Sensor
5-Boiler Door T
emp Sensor
6-
St
eam p
si 1 Sensor
7-
St
eam p
si 2 Sensor
8-
Boiler W
at
er Le
vel Sensor
9-
Supply
W
at
er
Le
vel Sensor
10-
Fuel Le
vel Sensor
11-
Fuel Pump p
si Sensor
12-
Pr
opane p
si Sensor
13-
No
zzle 1 p
si Sensor
14-
No
zzle 2 p
si Sensor
