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Finned copper tube gas boilers & water heaters – Boiler Manual
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6. If the second ignition att empt is unsuccessful the gas valves will
lockout, but the blower, pump and power venter will remain
on. To reset the boiler/water heater, take one of the following
steps:
• Adjust the high limit down below the point at which the
blower shuts down, then reset the limit to its normal sett ing.
• Remove power from the boiler/water heater, wait 30 seconds
and re-establish power to the unit.
7. On CSD-1 applications the blower and power venter will shut
down and the boiler/water heater will lock out. Th e unit must
be manually reset.
Main Burner:
1. Once the pilot is proved the MV terminal on (FSM) is energized
sending 24V ac to the main gas valve.
2. Th e main gas valve opens via action of K1.
3. Th e main burner indicator light illuminates. Th e PV terminal
remains energized and the pilot indicator remains on.
Normal Operation
• Staging will be controlled from the staging controller.
• Th e front control panel separately monitors limit, gas pressure,
water fl ow and airfl ow.
• If staging changes during operation, the blower, pressure switches
and gas valves will be switched or turned off as required.
• Stage 1 will operate fi rst and last.
For a change from stage 1 to 2, a 10 second DOM
time delay is provided in the pressure switch switching
circuit (TDR2). Th e time delay provides a hold state
that allows the blower to reach full speed and close
the high fi re pressure switch before it is energized to
confi rm proper air fl ow.
Demand Satisfi ed:
1. Stage switch 1 opens, TDR1 de-energizes.
2. Power is removed from ignition module, blower and power venter.
3. All indicator lights turn off except for the power indicator light.
4. Staging controller initiates a pump purge for 20 or more seconds,
depending on the inlet/outlet temperatures and ∆T sett ing in
the controller. Th e pump then shuts off .
Staging Control Alarms:
1. Staging control alarms are visible on the controller's LCD screen.
See the staging control documentation for details.
2. A powered alarm contact (2A max @ 24 VAC) is available to
provide an audio or visual indication of faults related only to the
staging control's operation. Th is contact is wired to the junction
box for optional remote indication. Refer to the 2 stage connec-
tion diagram for tie-ins.
High Limit, Low Water Flow, Low Gas Pressure, High Gas
Pressure, Power Venter Interlock Faults
1. All gas valves, the blower and power venter will be off if either
alarm is tripped.
2. Th e manual reset high limit can be reset through a knockout
accessible in the left side jacket panel.
3. Condition indicators are visible on the control panel.
Low Air (Blocked Flue/Air Inlet)
• One of two pressure switches will monitor blower airfl ow.
• Air monitoring will begin at prepurge. If a low air condition is
present, power will not be supplied to the ignition module. Th e
blower will remain on and the low air indicator will remain on
for as long as stage 1 remains energized.
• A low air indicator is visible on the control panel.
OPERATION SEQUENCE, 4 STAGE
D1050 THROUGH D2100
Refer to the included connection and wiring diagrams
for further control system information.
POWER ON:
Demand for Heat:
1. BTC staging control starts pump and begins 50 second delay
before energizing Stage 1.
2. Stage switch 1 closes.
3. System checks primary limit and other interlocks. Will not start
if either switch is open.
Prepurge:
1. TDR1 energizes starting a 40 second prepurge cycle.
2. K4 energizes the low speed side of both blowers. If the side-wall
vent option is used the power venter is energized, closing the
power venter interlock. Th
e power vent indicator light illuminates.
3. Th e low air indicator lights will remain lit until the blowers comes
up to speed. Th e indicator lights will turn off and prepurge
indicator light will illuminate when the pressure switches make.
4. At the end of the prepurge cycle TDR1 times out and the TDR1
N.O. contacts close sending 24V ac to the ignition control.
5. Th e prepurge indicator light shuts off .
6. K2 will switch the pilot valve, left main valve and blower to high
fi re or low fi re, depending on the staging.
7. K3 will switch the right main valve and blower to high fi re or low
fi re, depending on the staging.
