750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
5-15
5.10 — Control Operational Test and Checks
5.9.1 — 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. The hot flame to cool air
cycling subjects the pressure vessel metal and refractory to undesirable stresses.
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 the operating limit pressure or temperature is
reached, unless:
1. The burner is manually turned “off.”
2. The low-water condition is detected by low-water level control.
3. The electrical or fuel supply is interrupted.
4. The combustion air pressure or atomizing air pressure 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 flame failure 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. Refer to the “troubleshooting” section in Chapter 7.
5.9.2 — Shutdown
When the operating limit control setting is reached to open the circuit or if the burner switch is turned “off,” the
following sequence occurs:
1. The fuel valve is de-energized and the flame is extinguished.
2. The timer begins operation and the blower motor continues running to force air through the furnace in the
post-purge period.
3. At the end of the programmed post-purge period, the blower motor is turned off. The air pump motor of an oil
fired burner is also turned off.
4. The timer has returned to its original starting position and stops. The unit is ready to restart. See 5.10 — Con-
trol Operational Test and Checks
5.10 — Control Operational Test and Checks
Proper operation of the various controls should be verified and tested when the boiler is initially placed into ser-
vice, or whenever a control is replaced. Periodic checks should be made thereafter in accordance with a planned
maintenance program.
NOTE: There can be other reasons for shutdown such as motor overload, flame outage, tripped circuit breakers,
blown fuses, or through other interlock devices in the circuitry.
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