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BWF Control System – Sequence of Operation
(Refer to Figures 35 and 36 for BWF ladder and connection diagrams)
1) A call for heat from the thermostat energizes relay coil 1K (the relay on the R8285), causing contacts 1K1 and 1K2 to
make. Contact 1K1 starts the circulator. Contact 1K2 sends power to the high limit.
2) Assuming that the high limit is made, current will flow through the normally closed contacts on the pressure switch to
relay coil “2K” (the R8222 relay coil). Contacts 2K1 make, starting the combustion blower. Contacts 2K2 make, creating
a current path in parallel with the normally closed pressure switch contacts.
3) As the combustion fan comes up to full speed, the normally closed contacts on the vacuum switch break. Power remains
applied to the 2K coil, however, through the 2K2 contacts. Once the combustion fan has created an adequate vacuum at
the vacuum switch tapping, the normally open contacts on the pressure switch will make, sending power to the ignition
module via the normally closed flame rollout switch.
4) Upon application of voltage across the “24V” and “24V (GND)” terminals, the ignition module will enter a 30-second
pre-purge period. After 30 seconds has passed, the module will start an ignition spark at the pilot and apply 24 volts
across the pilot valve (terminals “PV” and “MV/PV”)
5) Once the pilot is established, the pilot flame will act as a diode, converting the AC current at the electrode to a half wave
DC current at the pilot’s ground strap. This DC current flows through the boiler to the “GND (BURNER)” connection on
the ignition module. For the ignition module to recognize that a pilot flame is present, the DC current flowing into this
terminal must be in excess of approximately 1.0 uA.
6) Once the ignition module detects the presence of a pilot flame, voltage is applied across the main valve (terminals “MV”
and “MV/PV”), opening the valve and establishing main flame.
7) If the ignition module does not detect the presence of a pilot flame after 90 seconds, the ignition spark will stop, the pilot
valve will close, and the ignition module will wait for approximately 5 minutes before restarting the ignition sequence.
During this time both the circulator and combustion fan will continue to run. If the pilot is never established, the ignition
sequence will continue to be restarted at 5-minute intervals.
8) Assuming that main flame is established, the boiler will fire until either the call for heat is satisfied or until the water
temperature exceeds the high limit setting. If the high limit setting is exceeded, relay coil 2K will be de-energized, turning
off the burners and combustion fan. The circulator will continue to run until the call for heat is satisfied, regardless of the
water temperature.
9) At the end of a burner cycle, the normally closed contacts on the vacuum switch should make after the fan is de-
energized. If this does not happen, there will be no current path to relay coil 2K upon the next call for heat and the boiler
will not fire.
10) The flame rollout switch is a normally closed thermal switch that is positioned at the burner compartment opening. In the
event that flames exit this opening, the flame rollout switch will open, de-energizing the ignition module and closing the
gas valve. Once opened, this switch must be replaced.