Finned copper tube gas boilers & water heaters – Boiler Manual
26
Normal Operation
• Staging will be controlled from the staging controller.
• The front control panel separately monitors limit, gas pressure,
water flow and airflow.
• If staging changes during operation, the blower, pressure switches
and gas valves will be switched or turned off as required.
• Stage 1 will operate first 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). The time delay provides a hold state
that allows the blower to reach full speed and close
the high fire pressure switch before it is energized to
confirm proper air flow.
Demand Satisfied:
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 setting in
the controller. The 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. This 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. The 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 airflow.
• Air monitoring will begin at prepurge. If a low air condition is
present, power will not be supplied to the ignition module. The
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. The power vent indicator light illuminates.
3. The low air indicator lights will remain lit until the blowers comes
up to speed. The 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 24VAC to the ignition control.
5. The prepurge indicator light shuts off.
6. K2 will switch the pilot valve, left main valve and blower to high
fire or low fire, depending on the staging.
7. K3 will switch the right main valve and blower to high fire or low
fire, depending on the staging.
Ignition Trial:
1. Once energized, the flame sense module (FSM) initiates 4 sec-
ond diagnostic cycle before sending 24VAC to the PV terminal
and energizing the ignition transformer.
2. The flame failure LED will be lit during the 4 second diagnostic
cycle unless the unit is configured for CSD-1. When the PV
terminal energizes, the LED will turn off. If the ignition trial
fails, the LED will relight.
3. The pilot valve and ignition transformer are energized for the
10 second ignition trial. The pilot indicator light illuminates
during this time.
4. If the ignition attempt is unsuccessful, the ignition module will
retry in 5 minutes.
5. Since the staging controller remains powered, it will continue
to stage up for as long as the call for heat exists. The blower,
pump and power venter will remain for as long as a call for heat
exists.
