Sequence of Operation
4-2
750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
4.2 — Circuit and Interlock Controls
The burner control circuit is a two-wire system designed for 115 Vac, 60 Hz, single-phase power.
The electrical portion of the boiler is made up of individual circuits with controls that are wired in a manner
designed to provide a safe system. The program relay provides connection points for the interconnection of the
various circuits.
The controls used vary depending upon the fuel burned and the specific requirement of applicable regulatory bod-
ies. Refer to the boiler wiring diagram to determine the actual controls provided. The circuits and controls normally
used in the circuits are listed below and are referred to in the following sequence of operation.
Circuit Components/Controls
Limit Circuit
• Burner Switch (BS)
• Operating limit control (OLC) - pressure or temperature
• High limit control (HLC) - pressure or temperature
• Low-water cutoff (LWCO)
• Gas-oil selector switch (GOS) - combination burner only
• Oil drawer switch (ODS) - oil burner
• Low oil temperature switch (LOTS) - Nos. 5 and 5 oil only
• Low gas pressure switch (LGPS)
• High gas pressure switch (HGPS)
• LE Proximity switch interlock
• Fuel valve interlock circuit
• Main gas valve auxiliary switch (MGVAS)
• Oil valve auxiliary switch (OVAS)
Blower Motor Starter Circuit
• Blower motor starter (BMS)
• Combustion air proving switch (CAPS)
• Atomizing air proving switch (AAPS) - if provided
Running Interlock Circuit
• Blower motor starter interlock (BMSI)
• Combustion air proving switch (CAPS)
• Atomizing air proving switch (AAPS) - if provided
Running Interlock and Limit Circuit
• Low oil pressure switch (LOPS)
• High oil pressure switch (HOPS)
• High oil temperature switch (HOTS)
• Auxiliary low-water cutoff (ALWCO)
Low Fire Proving Circuit
• Low fire switch (LFS)
Pilot Ignition Circuit
• Gas pilot valve (GPV)
• Ignition transformer (IT)
• Gas pilot vent valve (GPVV) - if provided
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