A.O. Smith 2500, 200, 201, 2100, 1850, 1300 Control System, Description of MULTI-STAGE Firing System

CONTROL SYSTEM

DESCRIPTION OF MULTI-STAGE FIRING SYSTEM

The Central Control Board (CCB) is responsible for staging the Ignition Control Boards (ICB) and monitoring safety limit devices, control of circulation pump, power vent, alarm output and IRI gas valves (only on IRI models). The thermostat also resides on the CCB with inputs available for inlet, outlet and tank temperature probes as well as an input for a remote 24 VAC thermostat. The CCB has a display interface which connects to the Display Board to show system status and failures. The CCB also has a set of DIP switches which allows the user to control several system parameters. (See Figure 14.)

Each stage requires an Ignition Control Board (ICB) which is responsible for controlling a combustion blower, hot surface igniter and gas valve. Each ICB is capable of monitoring gas valve power, gas valve relay, flame sense and igniter current. The ICB is designed to communicate with the Central Control Board (CCB). Each ICB consists of identical hardware and software. Each stage ICB is made unique through the use of circuit board jumpers which allow the user to control such variables as stage identification and blower/igniter usage. (See Figure 15 for jumper configurations.)

These jumpers are pre-set at the factory and should only be adjusted by a qualified service technician.

The Display Board allows the end user to monitor water temperature, set-points, differentials, options, fault indications and error codes. Display Board pushbuttons labeled "ADJUST", "SELECT" AND "ENTER/RESET" enable the user to adjust set-points, differentials, post-circulate time, reset the cycle count and reset the control system during lock-out. Changes made to programmable features are stored in non-volatile memory.

DIA-SCAN II DISPLAY BOARD OPERATING PROCEDURES

The Display Board provides a user-friendly interface to the Central Control Board. With the Display Board, the user can control appliance functions and view the overall operating status of the appliance. If an error condition occurs, the Display Board will indicate the nature of the fault by illuminating a red LED. The display will further define the fault by illuminating a red LED corresponding to the stage on which the fault has occurred. Red and green LEDs are associated with each stage to indicate either a fault or normal operation. If the fault continues until the unit "locks out", the display will show a three digit code in addition to the red LEDs. (See Table 19 for error code chart.) Under normal operating conditions, the four digit LED display on the Display Board will continuously illustrate the water temperature sensed at the inlet temperature probe. If dip

ON

SW1

1 2 3 4 5 6 7 8 A B C D E F G H

DIP SWITCH CONFIGURATION TABLE

SW1 OFF		ON	SELECTION:
A	3 STAGE	4 STAGE	EITHER 3 OR 4 STAGE SYSTEM
B	3 TRIALS	1 TRIAL	EITHER 3 OR 1
C	NOIRI	IRI	WHETHER SYSTEM IS IRI OR
	GAS VALVE	GAS VALVE	STANDARD
D	INLET	TANK	INLET OR TANK AS
			CONTROLLING PROBE
E	NO EXTERNAL EXTERNAL		WHETHER EXTERNAL
	THERMOSTAT	THERMOSTAT	THERMOSTAT IS USED

FOUTLET 210°F OUTLET 240°F OUTLETMAXIMUMTEMPERATURE

G	190°F	220°F	MAX. SET-POINTTEMPERATURE
H	DEGREES°F	DEGREES°C	EITHER °F OR °C FOR DISPLAYED
			TEMPERATURE

Figure 14. Central Control Board's Dip Switch Configuration and Options

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