A.O. Smith DB/DW-720-1810 Internal Contaminants, Precautions, Checking and Adjusting the Input

INTERNAL CONTAMINANTS

The system must be internally cleaned and flushed after a new or replacement unit has been installed to remove contaminants that may have accumulated during installation. This is doubly important when a replacement unit is installed into an existing system where Stop Leak or other boiler additives have been used.

All systems should be completely flushed with a grease removing solution to assure trouble-free operation. Pipe joint compounds, soldering paste, grease on tubing and pipe all tend to contaminate a system.

Failure to clean and flush the system can cause solids to form on the inside of the heat exchanger, can produce acid concentrations that become corrosive, can allow excessive amounts of air or other gases to form which could block circulation, foul system accessories and damage circulator seals and impellers.

It is recommended that after installation, the boiler and system when filled should include the proper percentage of cleaning solution related to approximate water volume of the system. Fire and circulate for about one hour and then flush clean with fresh water. Commercial grease removing solutions are available.

PRECAUTIONS

If the unit is exposed to the following, do not operate boiler until all corrective steps have been made by a qualified serviceman:

1.Exposure to fire.

2.If damaged.

3.Firing without water.

4.Sooting.

If the heater has been exposed to flooding it must be replaced.

IMPORTANT

ONLY QUALIFIED PERSONNEL SHALL PERFORM THE INITIAL FIRING OF THE HEATER. AT THIS TIME THE USER SHOULD NOT HESITATE TO ASK THE INSTALLER ANY QUESTIONS REGARDING THE OPERATION AND MAINTENANCE OF THE UNIT.

CHECKING AND ADJUSTING THE INPUT

NOTE: For high altitude installations, calculate the input rate in accordance with the procedure in the HIGH ALTITUDE INSTALLATIONS in the OPERATING INSTRUCTIONS section.

1.Attach a pressure gauge or a manometer to the gauge port. Check for correct manifold pressure. PRESSURE SHOULD NOT EXCEED VALUE INDICATED ON RATING PLATE.

2.Use this formula to “clock” the meter. Be sure that other gas consuming appliances are not ON during this interval.

3600

T x H = Btuh

T= Time in seconds to burn one cubic foot of gas. H = Gas heating value (Btu per cubic foot of gas). Btuh = Actual boiler input per hour.

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.

FIGURE 26

PILOT BURNER

The pilot flame should envelop 3/8 to 1/2 inch (10 to 12 mm) of the top of the insulated rod on the pilot burner, fig. 26. Normally, the pilot flame will be correct when the pilot manual valve is in the full “ON” position. Check pilot burner every 3 months for proper flame characteristics.

FIGURE 27

To adjust the pilot flame, remove the screw on the pilot gas regulator, fig. 27, to expose the adjustment screw. Turn the adjusting screw clockwise to increase the length of the flame or counterclockwise to decrease the length of the flame.

MAIN BURNER

Check main burner every three months for proper flame characteristics, fig. 28.

TYPICAL AND MAIN BURNER FLAMES

FIGURE 28

The main burner should display the following characteristics:

•Provide complete combustion of gas.

•Cause rapid ignition and carryover of flame across entire burner.

•Give reasonably quiet operation during initial ignition, operation and extinction.

•Cause no excessive lifting of flame from burner ports.

If the preceding burner characteristics are not evident, check for accumulation of lint or other foreign material that restricts or blocks the air openings to the burner or boiler.

NOTE: Cleaning of main burners.

Shut off all gas and electric to unit.

Complete burner tray assembly may be removed by disconnecting union assembly, pilot line connection at main burner and sliding tray out of cabinet.

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