MG & SG Series Boilers – Installation and Service Manual
17
Small adjustments to the input rate can be made by varying the manifold pressure. Normally it should be
adjusted no more than 0.2 inch w.c. for natural gas or 0.5 inch w.c. for propane from the manifold
pressure specified on the rating plate.
WARNING
Exceeding the allowable input rate can produce dangerous concentrations of carbon monoxide,
and cause the boiler to overheat resulting in severe personal injury, death or substantial
property damage. Carbon monoxide is a lethal, colorless and odorless gas.
Input Rate Test
Consult gas company to determine the heating value of the gas supplied in Btu per cubic feet. Operate
boiler for 15 minutes starting with all parts at room temperature and check input by clocking gas meter
with all other gas appliances turned off, including their pilot flames. Use the following formula:
INPUT (Btu/h) =
Clocked Seconds
Timed) FeetCubic of (Number x Gas) of Value(Heating(3600) ×
To ensure accuracy for rating, clock enough cubic feet of gas so that there is at least one revolution of the
test dial and the clocked time is at least 60 seconds.
Two Stage Gas Valve
When a two stage gas valve is used, it must be checked for correct input at both "High" and "Low" fire
settings. The clocked input rate MUST be within the "Minimum Input" and the "Input" as specified on the
boiler's rating plate. To force the boiler to low fire, unplug the blue wire from the "HI" (or "W-2") port of the
two stage gas valve. Perform the Input Rate Test described above and adjust manifold pressure of High
and Low settings as necessary. For altitudes above 2000 feet, DO NOT derate the "Minimum Input" rate.
3.7 CHECK FOR DRAFT HOOD SPILLAGE
WARNING
Continuous spillage at the draft hood relief opening may result in severe personal injury, death
or substantial property damage.
After the main burners have operated for 5 minutes, check to see that combustion products are going up
the chimney or gas vent properly by passing a lighted match (or smoke from a cigar, cigarette, or pipe)
around the edge of the relief opening of the draft hood. If the chimney or gas vent is drawing properly,
the match flame or smoke will be drawn into the draft hood. If not, the combustion products will tend to
extinguish this flame. While performing this test, make sure all exhaust fans, air movers, and gas
appliances are operating and doors and windows are closed. If the combustion products are escaping
from the relief opening of the draft hood, IMMEDIATELY shutdown the boiler and make proper
adjustments or repairs.
3.8 CHECK OF CONTROLS
After the unit has been operated for awhile, lower the aquastat setting below the setpoint and burner
should shut off. Rotate the aquastat higher than setpoint and the main burner should ignite. Return the
aquastat to its original setpoint and make sure boiler cycles normally. Repeat this type of check on the
safety high-limit aquastat, thermostat and other system controls to ensure all work satisfactorily. If any of
the safety or controls do not function, necessary corrections should be made immediately.
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