750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
2-21
2.15 — Modulating Firing
of the motor. The switch must be closed to establish that the damper and fuel metering valves are in the low-fire
position before the programmer commences into the ignition period. During this time, neither the manual flame
control nor the modulating control have any control over the damper motor, regardless of their setting.
An optionally equipped boiler uses a second integral switch to establish that the motor has driven the damper to an
open position during the pre-purge period. The second integral switch closes, as high-fire position is approached,
to complete an internal circuit in the programmer to allow continuation of the programming cycle.
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