Bradford White D Series Service Manual page 26

Conditions: Upper or Lower Sensor Reading
Faulty, High Water Temperature, or suspect
thermostat is not accurate.
Sensor Resistance Testing
Upper Sensor
1. Determine resistance value of upper sensor. Test across
grey wires.
2. Draw quart of water off T&P valve. Using a thermometer,
determine water temperature.
3. Use table below to verify correct resistance per water
temperature measured.
Lower Sensor:
1. Determine resistance value of lower sensor. Test across
center wire (common) to each outside wire. Resistance of both
thermisters in the lower sensor should be close to each other.
If the resistance values for both thermisters are not close to
each other, replace the lower sensor. The dual thermisters are
used to provide high limit protection in case the thermostat
circuit fails to shut off the water heater.
2. Draw quart of water off Drain Valve.
Using a thermometer, determine water temperature.
3. Use table below to verify correct resistance per water
temperature measured.
Are readings N
correct?
Y
Check harness
N
continuity.
Continuity okay?
Y
Replace
control board
Example: If water temperature is 84°F, then the resistance through the sensor would be 8449 (see shaded area).
°F 0
40 26109
50 19906
60 15314
70 11884
80 9299
90 7333
100 5827
110 4663
120 3758
130 3048
140 2488
150 2043
160 1688
170 1402
180 1170
190 982
200 828
26
Replace
thermister
Replace
harness
Be Careful When Making Resistance
Measurements Not to Damage or
Deform Connectors or Connector Pins.
Sensor Resistance at Various Temperatures
NOTE: Sensor resistance increases as the temperature falls.
In Degrees F
1 2 3
25400 24712 24045
19383 18876 18383
14925 14548 14180
11592 11308 11032
9078 8862 8653
7165 7000 6839
5697 5570 5446
4562 4464 4368
3679 3602 3527
2986 2925 2866
2439 2391 2344
2004 1966 1928
1656 1625 1595
1376 1351 1327
1150 1129 1110
965 949 933
814 801 788
SERVICE PROCEDURE D24-I
Thermostat Circuit Testing
Upper thermister location
(applicable models)
Checking resistance of
upper sensor
Lower thermister
access located inside
control box.
Checking resistance of
lower sensor (center and
outside pins)
CAUTION
4 5 6
23399 22771 22163
17905 17440 16990
13823 13477 13140
10763 10502 10248
8449 8250 8057
6683 6531 6383
5326 5208 5094
4274 4183 4094
3453 3382 3312
2808 2752 2697
2298 2253 2209
1891 1856 1820
1566 1537 1509
1303 1280 1257
1090 1071 1053
917 901 886
775 762 749
Page 26
10
11
7 8 9
21573 21000 20445
16553 16128 15715
12812 12494 12185
1000 9760 9526
7869 7685 7507
6238 6098 5961
4982 4873 4767
4006 3922 3839
3244 3177 3112
2643 2590 2538
2166 2124 2083
1786 1753 1720
1481 1454 1427
1235 1213 1191
1035 1017 999
871 857 842
737 725 713