750-96 (revised 2010)
Model CB Packaged Boiler Manual
4-13
4.10 — Startup, Operating, Shutdown: All Fuels
To properly perform this testing and adjusting, it is necessary that the burner be allowed to fire at maximum rate
sufficiently long enough to achieve desired results.
4.10.1 — Operating
Normal operation of the burner should be with the switch in the automatic position and under the direction of the
modulating control. The manual position is provided for initial adjustment of the burner over the entire firing range.
When a shutdown occurs while operating in the manual position at other than low fire, the damper will not be in a
closed position, thus allowing more air than desired to flow through the boiler. This subjects the pressure vessel
metal and refractory to undesirable conditions.
With the switch set at “auto,” the burner will operate on a modulating basis according to the load demand.
The burner will continue to operate with modulated firing until operating limit pressure or temperature is reached,
unless:
• The burner is manually turned “off.”
• Low water condition is detected by the low water level control.
• Current or fuel supply is interrupted.
• Pressure of combustion (or atomizing) air drops below minimum level.
When the burner is shut down normally, by either the operating limit control or by manually switching the burner
off, the load demand light no longer glows.
Shutdown through conditions causing safety or interlock controls to open will actuate the flame failure light (and
alarm, if so equipped) and the load demand light will remain lit. The cause of this type of shutdown will have to be
located, investigated, and corrected before operation can be resumed.
4.10.2 — Shutdown
When the operating limit control setting is reached to open the circuit or if the burner switch is turned “off,” the fol-
lowing sequence occurs.
The fuel valve(s) is de-energized and the flame extinguished. The timer begins operation and the blower motor con-
tinues running to force air through the furnace in the post-purge period.
At the end of the programmed post-purge period, the blower motor is de-energized. The air pump motor of an oil
fired burner is also de-energized. The timer has returned to its original starting position and stops. The unit is
ready to re-start.
NOTE: There can be other reasons for shutdown such as motor overload, flame outages, tripped circuit breakers,
blown fuses, or through other interlock devices on the circuitry.
It is advisable to check for tight shutoff of fuel valves. Despite precautions and strainers, foreign material in either new
or renovated fuel lines may lodge under a valve seat preventing tight closure. This is especially true in new installa-
tions. Promptly correct any conditions causing leakage.
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