Service Manual

3 Troubleshooting (continued)

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

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 Knight XL Installation and Operation Manual for correct terminal location.

Table 3-2A - Inlet Water/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

1223,893

1402,760

Table 3-2B - 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

Table 3-2C - Outlet Water Sensor Resistance vs. Temperature

 

 

 

S1a

 

 

 

 

S1b

 

 

 

 

 

(Wire Color - R/BK and Y)

 

 

 

 

(Wire Color - G and Y)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Temperature

 

Resistance

 

Temperature

 

Resistance

Temperature

 

Resistance

 

Temperature

 

Resistance

 

 

50

19,553

158

2,004

50

40,030

158

3,478

 

 

68

12,690

176

1,464

68

25,030

176

2,492

 

 

86

8,406

194

1,084

86

16,090

194

1,816

 

 

104

5,715

212

816

104

10,610

212

1,344

 

 

122

3,958

 

 

 

 

122

7,166

 

 

 

 

 

 

140

2,786

 

 

 

 

140

4,943

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 3-2D - Flue Sensor Resistance vs. Temperature

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

S3a

 

 

 

 

S3b

 

 

 

 

 

 

(Wire Color - W/B and Y)

 

 

 

 

(Wire Color - PR and Y)

 

 

 

 

Temperature

 

Resistance

 

Temperature

Resistance

Temperature

 

Resistance

 

Temperature

 

Resistance

 

 

50

 

40,030

 

158

 

3,478

50

 

258,500

 

158

 

16,870

 

 

68

 

25,030

 

176

 

2,492

68

 

125,500

 

176

 

12,000

 

 

86

 

16,090

 

194

 

1,816

86

 

80,220

 

194

 

8,674

 

 

104

 

10,610

 

212

 

1,344

104

 

52,590

 

212

 

6,369

 

 

122

 

7,166

 

 

 

 

122

 

35,270

 

 

 

 

 

 

140

 

4,943

 

 

 

 

140

 

24,160

 

 

 

 

 

35

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Lochinvar 400, 801 service manual Checking temperature sensors, Temperature Resistance Temperature Resistance

400, 801 specifications

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