MG & SG Series Boilers – Installation and Service Manual
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2.8 AUTOMATIC VENT DAMPER
This boiler is supplied with an automatic vent damper. The following instructions must be observed:
• The automatic vent damper should be installed at the top of the factory supplied draft hood (Figure 1 -
Alternate 3). No modifications to the automatic vent damper are permitted.
• The venting system must be arranged so that only the boiler is served by the automatic vent damper
with which it was supplied.
• Connect the wiring harness from the boiler to the automatic vent damper as indicated on the supplied
wiring drawings.
• The automatic vent damper position indicator should be clearly visible after installation.
• A minimum clearance of not less than 6 inches (153 mm) must be maintained between the automatic
vent damper device and combustible construction. Provision must be made for service access to the
automatic vent damper.
• The automatic vent damper must be in the open position when the boiler's main burner is operating.
• For orientation other than vertical, refer to automatic vent damper installation instructions
2.9 BLOCKED VENT AND FLAME ROLL-OUT SAFETY SWITCHES
All boilers with an input of 300,000 Btu/h and under are equipped with blocked vent and flame roll out
safety switches. The blocked vent safety switch is installed in the clip provided on the draft hood (Figure
1 - Alternate 1) or is mounted with screws (Figure 1 - Alternate 2). The blocked vent safety switch is pre-
wired at the factory either directly to the boiler controls (Figure 1 - Alternate 1 & 2), or through a wiring
harness for a boiler with an automatic vent damper (Figure 1- Alternate 3). If the vent becomes blocked a
boiler shut down will occur. Ensure that the vent is free of obstructions.
The flame roll out safety switch will cause a boiler shutdown if the heat exchanger becomes blocked with
soot or corrosion.
WARNING
Shut down of the boiler by either the “Blocked Vent” or the “Flame Roll-out” safety switch is an
indication that carbon monoxide may be improperly venting into the premises and the boiler
must be serviced by a qualified person who is capable of determining the cause of the shut
down and can take corrective action. Carbon monoxide is a lethal, colorless and odorless gas.
FIGURE 1 - MOUNTING LOCATION OF BLOCKED VENT SAFETY SWITCH AND WIRE ROUTING
ALTERNATE 1 ALTERNATE 2
ALTERNATE 3
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