Manual

SEQUENCE OF OPERATIONS
BOILER WITH TANKLESS COIL:
Aquastat high limit controller:
The aquastat control's high limit contacts open and turn off the
burner when the boiler water temperature reaches the control's
high limit set point. The high limit contacts automatically reset
after the boiler water temperature drops past the set point by
10°F, which is a fixed differential.
Aquastat low limit and circulator control:
With the adjustable differential at the minimum setting of IO°F:
• On a boiler water temperature rise above the low limit set
point, the burner circuit contacts (RB) break and the
circulator circuit contacts (RW) make
• On a boiler water temperature drop of 10°F below the low
limit set point, the RB contacts make and the RW contacts
break.
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With the adjustable differential setting greater than I O°F:
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When the boiler water temperature is at (or below) the low limit set point, the RB contacts make
and fire the burner and the RW contacts break leaving the circulator off. The burner will fire until
the boiler water temperature reaches the low limit set point plus the adjustable differential setting
minus 10°R At this point the RB contacts break stopping the burner and the RW contacts make.
With no call for space heating, operating in this way keeps the circulator off and allows the boiler
to give preference to the domestic water heating requirements. Example: Consider the boiler water
temperature drops to 150°F with the low limit set at 160°F and the differential is set at 15°E The
burner will begin to fire. When the aquastat probe senses a boiler water temperature of 165°F (15
°F-10°F = 5°F, then 160°F +5°F =165°F) the RB contacts break and the RW contacts make.
When the boiler water temperature rises above the low limit / adjustable differential setting
and the thermostat controls call for domestic space heating. The sequence of operation for
the burner and circulator is as follows:
1. Thermostat calls for heat, completing circuit between terminals T & T on the aquastat controller,
energizing the 1K relay coil.
2. With the 1K relay coil energized, contacts 1K1 and 1K2 are closed. Terminal B1 is energized, providing
power to the oil burner primary control. This, in turn, powers the ignition coil and burner motor.
3. With the primary control energized, the burner operation starts and remains running as long as the
cad celt senses flame. In the event of flame failure or the flame is not fully proven within the trial
for ignition period, the primary control wilt lockout and open the burner circuit. This will require a
manual startup of the burner.
4. As long as flame is proven through the cad cell relay, the burner will remain on until the circuit is
interrupted by the boiler water temperature reaching the aquastat's high limit setting (opening high
limit contacts RB), or the thermostat is satisfied breaking the T-T circuit.
5. Circulator pump is powered through terminal C 1 and will run when boiler water temperature is
above the low limit setting and there is a call for heat from the thermostat. If the boiler water
temperature reaches the aquastat's high limit setting and high limit contact RB is de-energized, the
burner stops but the circulator pump will continue to run, as long as, the thermostat calls for heat.
6. Whenever the boiler water temperature reaches the aquastat's high limit setting, the high limit contact
RB is de-energized shutting the burner off. Then the boiler water temperature must fall 10°F below the
aquastat's high limit setting for the high limit contacts RB to close and the burner to be energized.
7. When the thermostat is satisfied, the call for domestic space heating is ended. Relay coil 1K is de-
energized, opening 1K1 and 1K2 contacts. Both the burner and circulator pump operation stop.
NOTE: High limit setting must be a minimum °f 20° higher than the I°w limit setting I
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