Product Overview

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McDonnell & Miller #67 Low Water Cut-off - Interrupts burner operation if the water in the boiler drops below a safe level.
Burner operation is restored when the water level in the boiler is raised above the cut-off point.
The vent damper will close when the low water cut-off interrupts burner operation.
Pressure Limit Control - Interrupts burner operation when the pressure in the boiler exceeds the “Cut-in” setting plus the
differential setting. The “Cut-in” setting is shown on the outside of the control and is adjusted using the screw on the top of the
control. The differential is adjusted using the white thumb wheel on the inside of the control. Burner operation is restored when
the pressure in the boiler drops to the “Cut-in” pressure.
The vent damper will close when the pressure limit control interrupts burner operation.
Blocked Vent Switch (BVS)-Automaticallyinterruptsburneroperationintheeventthatuegasspillsfromthedraftdiverter
opening. This switch is equipped with a reset button which must be pressed to restore normal burner operation. An open blocked
vent switch is indicative of a problem with the vent system. If the blocked vent switch opens, the cause of the venting problem
mustbefoundandcorrectedbyaqualiedgasservicetechnicianbeforetheblockedventswitchisreset.
Flame Rollout Switch (FRS)-Automaticallyinterruptsburneroperationwhenamesorexcessiveheatarepresentinvestibule.
Theamerolloutswitchisasingleusedevicewhichmustbereplacedbyanidentical switch in order to restore normal operation.
Anopenamerolloutswitchisusuallyindicativeofapluggedheatexchanger.Thecauseoftheamerolloutmustbefound
andcorrectedbyaqualiedgasservicetechnician,andtheswitchreplacedwithanidentical one, before the boiler is returned to
operation.
X. Electrical (continued)