A.O. Smith 405, 400 Control System, Manifold Pressure, Adjustments, Risk of Scalds Temperature

MANIFOLD PRESSURE

The manifold gas pressure is measured at the pressure tap on the downstream side of the combination gas valve(s). For natural gas the Manifold Pressure should measure 3.5" W.C. For propane (LP) gas, the pressure should read 10" W.C.

IMPORTANT

UNDER NO CIRCUMSTANCES SHALL THE GAS PRESSURE MEASURED AT THE BURNER MANIFOLD EXCEED THAT STATED ON THE BOILER RATING PLATE. OVERFIRING WILL RESULT IN DAMAGE TO THE BOILER, AS WELL AS INCREASED RISK OF FIRE, SOOTING AND ASPHYXIATION.

ADJUSTMENTS

ON INITIAL STARTUP SOME ADJUSTMENTS ARE NECESSARY.

1. CHECK MANIFOLD AND INLET GAS PRESSURES.

TABLE 20. RISK OF SCALDS.

TEMPERATURE	TIME TO PRODUCE 2nd & 3rd
SETTING	DEGREE BURNS ON ADULT SKIN
OVER 170°F (77°C)	NEARLY INSTANTANEOUS
160°F (71°C)	ABOUT 1/2 SECOND
150°F (66°C)	ABOUT 1-1/2 SECONDS
140°F (60°C)	LESS THAN 5 SECONDS
130°F (54°C)	ABOUT 30 SECONDS
120°F (49°C) OR LESS	MORE THAN 5 MINUTES

USE ANTI-SCALD VALVE(S) in the hot water system to reduce the risks of scalding at points of use such as lavatories, sinks and bathing facilities.

CONTROL SYSTEM

2.CHECK THE INPUT. SEE NATIONAL FUEL GAS CODE, ANSI Z223.1 OR CAN/CSA - B149.1 (CURRENT EDITION) FOR PROCEDURES.

DANGER

HOT WATER TEMPERATURES REQUIRED FOR AUTOMATIC DISHWASHER AND LAUNDRY USE CAN CAUSE SCALD BURNS RESULTING IN SERIOUS PERSONAL INJURY AND/OR DEATH. THE TEMPERATURE AT WHICH INJURY OCCURS VARIES WITH THE PERSON'S AGE AND TIME OF EXPOSURE. THE SLOWER RESPONSE TIME OF CHILDREN, AGED OR DISABLED PERSONS INCREASES THE HAZARDS TO THEM. NEVER ALLOW SMALL CHILDREN TO USE A HOT WATER TAP, OR TO DRAW THEIR OWN BATH WATER. NEVER LEAVE A CHILD OR DISABLED PERSON UNATTENDED IN A BATHTUB OR SHOWER.

THE WATER HEATER SHOULD BE LOCATED IN AN AREA WHERE THE GENERAL PUBLIC DOES NOT HAVE ACCESS TO SET TEMPERATURES.

IT IS RECOMMENDED IN DOMESTIC HOT WATER APPLICATIONS THAT LOWER WATER TEMPERATURES BE USED TO AVOID THE RISK OF SCALDING. IT IS FURTHER RECOMMENDED, IN ALL CASES, THAT THE WATER TEMPERATURE BE SET FOR THE LOWEST TEMPERATURE WHICH SATISFIES THE USER'S HOT WATER NEEDS. THIS WILL ALSO PROVIDE THE MOST ENERGY EFFICIENT OPERATION OF THE BOILER AND MINIMIZE SCALE FORMATION IN THE HEAT EXCHANGER, THUS PROLONGING THE LIFE OF THE BOILER.

SETTING THE WATER HEATER TEMPERATURE AT 120°F (49°C)

WILL REDUCE THE RISK OF SCALDS. SOME STATES REQUIRE SETTINGS AT SPECIFIC LOWER TEMPERATURES. TABLE 20 ABOVE SHOWS THE APPROXIMATE TIME-TO-BURN RELATIONSHIP FOR NORMAL ADULT SKIN.

The EMC 5000 control system is a fully integrated, state of the art electronic control system. It consists of sensors, output devices, a power switch, a 24vac transformer, wiring and the following printed circuit boards:

•Central Control Board (CCB), see Figure 17.

•Flame Control Board (FCB), see Figure 18.

•Power Distribution Board (PDB), see Figure19.

•User Interface Module (UIM), see Figure 21.

The CCB contains circuitry for both master control and flame control for the first stage. The FCB's contains circuitry for control on up to three additional stages. Dipswitches on the CCB and FCB are used to configure the system. The User Interface Module (UIM) communicates with the user through a set of touch pads and a 4- line, 20-character LCD display. The PDB provides connection points for input power, the water pump, and the transformer. It also distributes power to the system and contains the system fuses.

Multiple-stage control is accomplished by means of an internal communications network between the CCB and the FCB's. One FCB is required for each stage beyond the initial first stage. The CCB also contains an external communications system to allow for connection to a PC, a modem, an EMS system, or something similar. Through this connection multiple boilers can also be linked together. CAUTION: The internal communications cables should never be connected to the external communications connectors and vice-versa.

There are several microcontrollers used on the boards. These micros control the temperature and ignition control functions for the boiler. Inherent in the design are the normal operating sequences and safety features associated with a gas ignition control system. The system 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 display a red fault light as well as indicate the cause of the fault on the display. The operating programs for the system are stored in permanent memory inside the micros. User-selectable operating parameters and a history of detected faults are stored in re-writable memory in the micros. A loss of power does not affect either of the memories.

Inputs to CCB and FCB

Temperature Sensors:

• Temperature probes (CCB - outlet and either inlet or tank are

34