Line Polarity Indicator, Fuse Protection

ELECTRONIC HOT SURFACE

IGNITION CONTROL BOARD

ALL MODELS - The WHC1502 ignition control board is a fully integrated, state of the art electronic control system. The ignition control board includes a microprocessor, which governs all temperature and ignition control functions for the appliance. Inherent in the design are the normal operating sequences and safety features associated with a gas ignition control system. The ignition control continuously performs various diagnostic tests to verify proper appliance and control operation. Should an unsafe condition occur, the control will shut down the burner and illuminate the appropriate diagnostic indicators on the Display Board, indicating a need for service. All operating programs are stored in permanent memory on the ignition control and a second programmable memory is used for retaining user-specific operating parameters in the event main power is ever interrupted.

Line Polarity Indicator

A green LED is mounted on the ignition control to indicate line volt- age polarity is properly connected. When 120 VAC input power is properly connected to the Ignition Control Board, the green LED will illuminate. If an error is made when connecting 120 VAC input power, this LED will not light. Improperly connecting the input power may result in a false flame sensor failure.

Fuse Protection

The 24 VAC circuitry is protected with a 3 amp auto fuse. If the fuse opens, a red LED located near the fuse will light. If the red LED is illuminated, replace the fuse (recommended replacement part is Little fuse p/n 257003 automotive fuse). Repeated failure of the fuse is an indication of possible damage to the ignition con- trol board.

NOTE: One extra fuse is supplied with the boiler.

Typical Control/Appliance Operating Sequence

1.When power is applied to the WHC1502 ignition control, the Display board will initially run through a self-diagnostic routine, and then go into its operating mode, displaying the temperature sensed at temperature probe #1 (Out- let).

2.If the ignition control board determines the actual outlet water temperature at the temperature sensing probe (probe #1) is below the programmed temperature set-point less the switching differential, and the thermostat circuit or tank probe circuit closes, call for heat is activated.

3.The ignition control board then performs selected system diagnostic checks. This includes confirming the proper state of the ECO/High Limit device, flow switch, and pres- sure switches.

4.If all checks are successfully passed, the circulating pump circuit is energized, then the combustion blower is ener- gized for the 20 second pre-purge cycle.

5.When the pre-purge cycle is complete, the ignitor is ener- gized. The pump and blower should continue to run.

6.The ignition control board will verify ignitor current. After the verification, the gas valve will open, allowing gas to enter the burner.

7.After an additional 1 second, the ignition control board will monitor the flame sense probe to confirm a flame is present. If a flame is not verified within 4 seconds, the gas valve is immediately closed, and the ignition control board will return to step 2, unless jumper J30 is in place (ON), see figure 2.

8.If a flame is confirmed, the control will enter the heating mode where it will continue heating until the set-point tem- perature is reached, and the thermostat circuit opens. At that point, the gas valve is closed and the control enters the post-purge and post-circulating cycles.

9.The combustion blower will run for a 25 second post purge cycle. When the post purge cycle is complete, the blower is de-energized and will coast to a stop. The circulating pump will continue with the post-circulate cycle for the selected amount of time, factory default is 45 seconds. See circulating pump adjustment procedure on page 5 and 6 of this manual.

10.The control now enters the idle state while continuing to monitor temperature and the state of other system de- vices. If the outlet temperature drops below the set-point value minus the switching differential, and the thermostat circuit or tank probe circuit closes, the control will auto- matically return to step 2 and repeat the entire operating cycle. During this idle state, if the control detects an im- proper operating state for external devices such as the ECO switch, air pressure switch, gas pressure switch, etc., the appropriate LED(s) on the Display Board will illu- minate indicating the nature of the fault.

DIA-SCAN II DISPLAY BOARD OPERATING PROCEDURES

The Display Board provides a user-friendly interface to the WHC1502 Ignition Control Board. With the Display Board, the user can control appliance functions and view the overall oper- ating status of the appliance. If an error condition occurs, the Display Board will scroll a message across the LED display, indicating the error code. Under normal operating conditions, the four digit LED display on the Display Board will continuously illustrate the water temperature sensed at temperature probe #1 (Outlet). The push buttons on the Display Board allow the user to program and view the desired water temperature set point. The Display Board is connected to the Ignition Control Board through a 6 conductor cable assembly with modular plug terminations. In addition, an 8 conductor modular jack on the Display Board allows for connecting a remote display board.

When power is applied to the WHC1502 System, the Display Board will initially run through a self-diagnostic test, and then display the Outlet temperature. To display a specific setting or temperature, press the SELECT push-button until the appropriate LED is illumi- nated (see figure 1). After 5 seconds, the Display Board will auto- matically revert to displaying the Outlet temperature. Pressing the ENTER/RESET push-button will hold the display in the indicated mode until the SELECT push-button is pressed.

With the Display Board, the user can make adjustments to many of the appliance’s control features. This includes the following:

Options/Features Setting Procedures

•Set Appliance Temperature Set-point Value

•Set Appliance Switching Differential Value

•Select Appliance Post-Circulate Time

•Set Appliance Circulating Pump to Continuous ON Mode

•Check Appliance Cycle Count

•Control the water temperature in a storage tank

GB/GW-500, GB/GW-650, GB/GW-750, GB/GW-400, GB/GW-200 specifications

A.O. Smith is a renowned name in the water heating industry, offering a wide range of products that cater to various residential and commercial needs. Among their standout offerings are the GB/GW-200, GB/GW-400, GB/GW-650, GB/GW-750, and GB/GW-500 models. Each model is designed with advanced technologies, ensuring optimal performance, energy efficiency, and reliability.

The GB/GW-200 model, with a capacity of 200 liters, is ideal for small to medium-sized households. It features a high-efficiency gas burner and an advanced electronic control system that ensures accurate temperature regulation. The unit also comes equipped with a glass-lined tank for enhanced durability and resistance against corrosion, extending its lifespan significantly.

Moving up in capacity, the GB/GW-400 model offers 400 liters of hot water storage, making it a preferred choice for medium to large households or small businesses. One of its key features is the multiple safety systems integrated into its design, including flame failure protection and temperature control features, making it both safe and reliable. Additionally, this model is equipped with a user-friendly digital display that allows for easy monitoring and adjustments.

The GB/GW-500 model takes it a step further with a capacity of 500 liters. Designed for larger applications, including commercial settings, it integrates A.O. Smith’s innovative heating technology for rapid recovery rates. This model stands out with its focus on energy efficiency, having an impressive Energy Factor rating that significantly reduces operational costs.

The GB/GW-650 and GB/GW-750 models cater to even larger needs, featuring capacities of 650 and 750 liters respectively. Both models are engineered with high-output burners, ensuring quick heating even during peak demand periods. Advanced insulation materials are used, enhancing thermal efficiency and minimizing heat loss, which translates to significant energy savings over time.

All these models feature A.O. Smith’s proprietary tankless technology, which allows for continuous hot water supply without the need for a large storage tank. This innovation not only saves space but also addresses the ever-increasing demands for hot water in modern households and businesses.

In conclusion, the A.O. Smith GB/GW series—GB/GW-200, GB/GW-400, GB/GW-500, GB/GW-650, and GB/GW-750—delivers reliable, energy-efficient water heating solutions suited for a variety of applications. With advanced safety features, user-friendly controls, and high energy efficiency ratings, these models are built to meet the demands of any modern water heating application, ensuring customer satisfaction and peace of mind.