A.O. Smith BTH 300A, BTH 400A warranty Sequence of Operation, Self Diagnostic Controller

OPERATION

SEQUENCE OF OPERATION

Typical Control/Appliance Operating Sequence

1.When the control is powered, it should first display “0”, then the input line voltage (“120”), the calibration setting (12), then the actual water temperature in the tank.

2.If the control determines that the actual water temperature inside the tank is below the programmed temperature setpoint less the differential, a call for heat is activated.

3.The control then performs selected system diagnostic checks. This includes confirming the proper state of the air switches and ECO limit device.

4.If all checks are successfully passed, the combustion blower is energized for the pre-purge cycle.

5.When the pre-purge cycle is complete, power is applied to the ignitor element for the ignitor warm-up period.

6.At the conclusion of the igniter warm-up period, the gas valve will open, allowing gas to enter the burner chamber.

7.The igniter will remain on for a short predetermined time period, then will be turned off.

8.After an additional 2 seconds, the control will monitor the flame sense probe to confirm a flame is present. If a flame is not verified within this time period, the gas valve will immediately be closed, and the blower will continue to run for approximately 10 seconds. The control will then return to step 2.

9.If a flame is confirmed, the control will enter the heating mode where it will continue heating the tank water until the setpoint temperature plus differential is reached. At this point, the gas valve is closed and the control enters the post-purge cycle.

10.The combustion blower will run for the duration of the post purge cycle to purge the system of all combustion gases. When the post purge cycle is complete, the blower is de-energized and will coast to a stop.

11.The control will now enter the idle state while continuing to monitor the internal tank water temperature and the state of other system devices. If the temperature drops below the setpoint value less differential, the control will automatically return to step 2 and repeat the entire operating cycle. During this idle state, if the control detects an improper operating state for external devices such as the ECO switch, vent switch, pressure switch, etc., the appropriate LED(s) on the Display Board will be illuminated indicating the nature of the fault.

SELF DIAGNOSTIC CONTROLLER

This controller is designed for ignition lockout after three consecutive failed attempts to light. If lockout occurs, the display lights will match Figure 17. Along with this, a numeric message will appear in the display. The following list of ERROR CODES illustrates possible numeric failures.

FIGURE 17.

GAS VALVE LED FLASHING

This condition results from a failure to establish burner ignition after three successive trials. In such cases:

1.Investigate the possible cause and remedy any observations.

2.Momentarily depress the button on the display panel to reset the lockout condition.

3.Confirm proper appliance operation.

	Possible Cause		Remedy
1.	Burner ground wire broken	1.	Check wire and connection
	or corroded		at burner
2.	Connectors unplugged	2.	Check connections
3.	Igniter broken	3.	Replace igniter
4.	Flame probe faulty	4.	Replace flame probe
5.	Gas shut off	5.	Turn on gas supply
6.	Clogged gas valve	6.	Replace gas valve
7.	Faulty gas valve	7.	Replace gas valve
8.	Defective control	8.	Replace control
9.	Burner improperly adjusted	9.	Adjust burner
10. Dirty burner		10. Clean burner

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