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Finned copper tube gas boilers & water heaters – Boiler Manual
27
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Ignition Trial:
1. Once energized, the fl ame sense module (FSM) initiates 4 sec-
ond diagnostic cycle before sending 24V ac to the PV terminal
and energizing the ignition transformer.
2. Th e fl ame failure LED will be lit during the 4 second diagnostic
cycle unless the unit is confi gured for CSD-1. When the PV
terminal energizes, the LED will turn off . If the ignition trial
fails, the LED will relight.
3. Th e pilot valve and ignition transformer are energized for the
10 second ignition trial. Th e pilot indicator light illuminates
during this time.
4. If the ignition att empt 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. Th e blower,
pump and power venter will remain for as long as a call for heat
exists.
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.
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 air fl ow.
• If staging changes during operation, blowers, pres-sure switches
and gas valves will be switched or turned off as required.
• Stage 1 will be on fi rst, last and whenever the boiler operates.
For a change from stage 2 to 3 or 3 to 4, 10 second
DOM time delays were added to the pressure switch
switching circuits (TDR2 and TDR3). Th e time delays
provide hold states that allow the blowers to reach full
speed and close the high fi re pressure switches before
they are 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, blowers and power venter.
3. All indicators (except power) off .
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
staging control operation. Th is contact is wired to the junction
box for optional remote indication. Refer to the 4 stage wiring
diagram for tie-ins.
High Limit, Low Water Flow, Low Gas Pressure, High Gas
Pressure, Power Venter Interlock Faults
1. All gas valves, the blowers and power venter will de-energize 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 the airfl ow of each
blower.
• Air monitoring will begin at prepurge.
• If a low air condition is present on the left side, power will not be
supplied to the module. Th e blowers will remain on and the low
air indicator will remain on for as long as a call for heat exists.
• If a low air condition is present on the right side, power will not
be supplied to the right gas valve.
• A low air indicator for each boiler side is visible on the control
panel.
