Bradford-White Corp D38T155 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.

With power on to water heater,

3

Verify Primary and secondary voltage at

the transformer

(see photo 3)Rear terminals primary

(120 VAC)

THERMOSTAT CIRCUIT BY-PASS
Turn power “OFF” to water heater and	Forward terminals
	secondary
locate thermostat board inside control box
	(24 VAC)
of water heater. Disconnect YELLOW wires
from the thermostat board at location
“N.O.” & “COM”. Use a jumper to connect
these two wires together
(see photos 4 & 5).	DANGER

Do not leave thermostat jumper in

place for normal operation.

Turn power on to water heater.		N	Verify transformer voltage
Does LED on ignition module illuminate?
			(see photo 3)
(see photo 6)
	Y
Does pilot and main burner operate?		N	See pilot operation testing
			(page 8)

	Y				LED Location
Turn power “OFF”.		6
Remove jumper and re-connect wires to
thermostat board. Wires are identified for
proper connection to board.
Disconnect ORANGE potentiometer (temp
adjustment dial) wires from thermostat
board (see photo 7)
			N
Check potentiometer for proper resistance values of:				Replace potentiometer
Greater then 4800 Ohms with dial at minimum setting.
Less than 50 Ohms with dial at maximum setting.
	(see photo 8).				Check Thermisters
	Are readings correct?
			Y		(see page 7)

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