A.O. Smith BTH 120-250(A) Self Diagnostic Controller, Sequence of Operation, Item Description

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ITEM DESCRIPTION

1.Transformer

2.Control Board & Cable Ass'y

3.E.C.O./Temperature Probe

4.Blower Proving Air Switch

5.Low Voltage Cable Assembly

6.

Line Voltage Cable Assembly

14.

Tubing-Pressure

7.

Blower/Motor Assembly

15.

Tubing-Pressure

8.

Igniter Assembly

17.

Switch-On/Off

10.

Control Display Board

18.

Low Gas Pressure Switch

11.

Blocked Outlet Exhaust Switch

 

(BTH 120 and 250 Only).

12.

Lower Temperature Probe

19.

Bocked Inlet Switch

13.

Wire Assembly-Gas Pressure

20.

Wire Assembly-Air

 

Switch

 

Flow Switch

FIGURE 17

OPERATION

SEQUENCE OF OPERATION

Typical Control/Appliance Operating Sequence

1.When the control is initially powered, it enters a test mode and will display the current software revision (example "104") for approximately 2 seconds, then "88.8" and all the LED's will illuminate for approximately 2 seconds. At this point, the control is in the idle mode and will display the actual tank temperature.

2.If the control determines the actual water temperature inside the tank is below the programmed temperature setpoint less one half 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 switch, ignitor, gas valve, flame sense rod, 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 (blower should continue to run).

6.During the ignitor warm-up period, the control will sense ignitor current. If ignitor current is within the specified range, the controller will energize (open) the gas valve at the end of the ignitor warm-up period, allowing gas to enter the burner chamber. If ignitor current is not within the specified range, the control will not energize the gas valve, and the control will return to Step 2 of the process. (See section below: Appliance Ignition Failure).

7.After energizing the gas valve, the control will keep the ignitor on for a short predetermined time period, then remove power to the ignitor.

8.After an additional 1 second, 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 controller will immediately de-energize (close) the gas valve, and return to step two of the process. (See section below: Appliance Ignition Failure).

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 one half the 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 internal state of the controller. If the temperature drops below the setpoint value less one half the differential, the control will automatically return to Step 2 and repeat the entire operating cycle.

SELF DIAGNOSTIC CONTROLLER

A green LED is mounted on the Main Control Board to indicate line voltage polarity is properly connected. The green LED is mounted next to connector CN1 (Line input connection). When 120 VAC input power is properly connected to the Main 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 sensor failure.

The 24 VAC circuitry is protected with a 3 amp auto fuse. If the fuse opens, the LED display and discrete LED's on the Display Board assembly will not illuminate. The recommended fuse replacement part is Littlefuse p/n 257003 automotive fuse. Repeated failure of the fuse is an indication of possible damage to the Main Control Board. If repeated fuse failure occurs, return the Control Board for service.

Under normal operating conditions, should the ignitor current fall out of specification or the gas fail to light at the burner during the first trial for ignition, the control will perform two (2) more ignition trials prior to entering a lockout state. Note that each subsequent ignition trial will not occur immediately. After a failed trial for ignition, the controller will remove all power from the blower, gas valve, and ignitor and return to the call for heat state. If a call for heat is activated, the controller will energize the combustion blower for the pre-purge cycle, and again activate the ignitor to complete its warm-up period. After the warm-up period, the gas valve is opened, ignitor power removed, and the control will again check for flame.

If ignition is sensed during any one of these trials, normal operation will resume. If ignitor current should fall out of specification or flame is not sensed after the third ignition trial, the control will automatically enter a lockout state ("Loc" displayed on the Display Board) and the ignitor or gas valve LED on the Display Board will flash. The lockout state is manually reset by momentarily pressing the push-button on the Display Board. If a manual reset does not occur within a one hour time period, the controller will automatically reset the lockout condition and provided the call for heat still exists, will attempt another ignition sequence.

FIGURE 18

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Contents What to do if YOU Smell GAS Cyclone XHE Model BTH 120-250AInput Cyclone XHE BTH 120 250 ROUGH-IN-DIMENSIONSForeword BTH-120 NPT BTH-150 199Features Table of ContentsInstallation Instructions Clearances Locating the HeaterMechanical Exhausting of Room AIR Hard WaterAIR Requirements Chemical Vapor CorrosionHorizontal Vent Direct Vent6cm 45 PVC Elbow with Mesh Screen Direct Vent Terminal InstallationDirect Venting Transmitted Into the Living SpacesVent terminals supplied with the heater must be used Installation SequenceInstallation of Vent System Vertical Vent Terminal InstallationControls and Switches Blower Prover SwitchVent Pipe Preparation GAS Piping System Connections Closed System WHC1202 Integrated Water Heater Control Connection DiagramHeater Wiring Water Line ConnectionsItem Description Self Diagnostic ControllerOperation Sequence of OperationNo Incoming Line Voltage Line LED Off Fault ConditionsTemperature Probe Fault Figure GAS Valve LED FlashingECO Switch Open Figure Control BAD FigureCombustion AIR Blockage Figure Initial START-UP Adjustment ProcedurePrior to Start UP Operating InstructionsFor Your Safety Read Before Operating General Information MaintenanceSediment Removal Anode Inspection and ReplacementFlushing DrainingDrain Valve and Access Panels Vent SystemTo inspect or replace an anode Installation Diagrams Install in Accordance with Local Codes Must be Identical Heaters Pipe Relief Valve to Open Drain Page Manifold Kits TROUBLE-SHOOTING Checklist and Service InformationNoisy Burner Operation Replacement PartsMotor will not RUN Motor RUNS, Burner Lights Momentarily Then Locks OUTALL Other Parts Service and Repair ExpensesClaim Procedure TankSmith Water Products Company

BTH 120-250(A) specifications

A.O. Smith BTH 120-250(A) is a cutting-edge water heater designed to meet the demands of residential and commercial settings. This high-efficiency unit is equipped with a range of features aimed at maximizing performance and minimizing energy consumption, making it a popular choice among homeowners and builders alike.

One of the standout features of the A.O. Smith BTH 120-250(A) is its energy efficiency. It operates with a thermal efficiency rating of up to 96%, which means that a significant portion of the fuel consumed is converted into usable hot water. This not only reduces energy bills but also lessens the environmental impact of water heating.

The unit employs advanced condensing technology, which captures and utilizes the heat from flue gases that would otherwise be lost in traditional units. This technology allows for lower exhaust temperatures and the potential for venting through PVC, significantly simplifying installation in various settings.

With a capacity range of 120 to 250 gallons, the BTH series is versatile enough to serve different needs. It is suitable for multiple applications, including large residential homes, commercial businesses, and industrial installations. The varying sizes ensure that it can deliver adequate hot water supply, even during peak demand periods.

In addition to its impressive capacity and efficiency, the A.O. Smith BTH 120-250(A) features a user-friendly digital control system. This allows users to easily set and monitor water temperatures, helping to prevent scalding and ensuring consistent comfort. The integrated diagnostics system alerts users to potential issues, facilitating proactive maintenance and reducing downtime.

Another appealing characteristic of this water heater is its durable construction. Built with high-quality materials, it is designed to withstand the rigors of frequent use while maintaining optimal performance over time. Furthermore, it comes equipped with an innovative flame rollback feature, enhancing safety by reducing the risk of flashback.

Overall, the A.O. Smith BTH 120-250(A) stands out in the competitive water heater market due to its exceptional efficiency, advanced technologies, and robust construction. Whether for residential or commercial use, this model provides reliable hot water supply while promoting energy savings and environmental sustainability. Its combination of performance and user-friendly features makes it a top choice for those seeking a reliable water heating solution.
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