Bradford-White Corp D-38T-155 service manual Service Procedure D24-I, Thermostat Circuit Testing

SERVICE PROCEDURE D24-I

Thermostat Circuit Testing

DANGER

120 volt exposure. To avoid personal injury, use caution while performing this procedure.

CAUTION

Be Careful When Making Voltage

Measurements or Jumping Terminals

Not to Damage or Deform Connectors or

Connector Pins.

This procedure assumes the flue damper is in working order. Be sure damper opens under its own power when the thermostat circuit is by-passed. Damper must be open or removed during this test. Do not force damper open using your hands or tools.

Condition: Water Heater Not Operating

Display shows error code “31” (Upper Sensor

Readings Faulty) or error code “32” (Lower Sensor

Readings Faulty)

Unplug or disconnect electrical power to the water heater

Check continuity of wire harness to affected sensor. Measurement of ohmeter should be close to 0 ohms. Replace wire harness if high resistance is measured (over 0.5 ohms) Check wires for intermittent connections, shorts, frayed insulation. Replace if necessary

(see photo 8)

If wire harness checks out O.K.check resistance of sensor. Refer to section on Sensor Resistance Testing. If sensor resistance is not near the values shown in the table, then replace upper or lower sensor as indicated by error code number.

Turn power on to water heater.

Run water heater through heating cycle and verify proper operation.

Sensor temperature can be viewed when burner shuts off (see

section on viewing the display in “Service Mode”.

Condition: Water Heater Not Operating

Display shows error code “65”

High Water Temperature (over 200 deg. F)

Measuring upper

7 sensor resistance through wire harness (disconnected at control board).

8Checking continuity of upper sensor wire harness.

Removing lower

9 sensor from well. Held in place by a clip fastened to well shoulder.

WARNING!

Do not reset the display from the hard lockout

state without correcting the cause of the

overheating condition.

Turn power “OFF”.

Draw water to cool tank below 120 deg. F

Check lower sensor. Is the sensor fully inserted into the well?	N
Sensor is held in place with a clip fastened to the well (see photo 9)
Check lower sensor wire making sure it is not damaged or has
breaks in the wire insulation. Check upper harness wires to upper
sensor, if used (some models).	Y
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If sensor clip is damaged

replace clip. Replace lower See next page sensor if damaged.

Check Sensor Resistance (see “Sensor Resistance Testing” section & photo 7)

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