Finned copper tube gas boilers & water heaters – Boiler Manual
25
OPERATION SEQUENCE, 2 STAGE OPTION
600 THROUGH 2300
Refer to the wiring diagram included with the unit
for further control system info.
POWER ON:
Demand for Heat:
1. The low operator switch closes, energizing pump delay timer
TD4 and the water pump(s).
2. Water flow through the unit closes the water flow switch contacts
energizing blower delay timer TD3.
3. The system checks all primary limit(s) and other inter-locks
before starting pre-purge. The unit will not start if any switch
is open.
Prepurge:
1. Blower delay timer TD3 energizes the low speed windings of
the blower(s).
2. Once sufficient air pressure in the combustion chamber is sensed
the pressure switch closes allowing the blower delay timer TD1
to start a 10 second pre-purge.
Ignition Trial:
1. Blower delay timer TD1 times out and the flame sense module,
FSM, is energized.
2. The FSM starts the 10-second ignition trial, energizing relay
R7, the pilot solenoid valve and the spark generator.
3. The pilot valve and spark generator are energized for the
10-second ignition trial. When the pilot flame is sensed, the
FSM sends 24VAC to its MV terminal energizing the safety
and low fire-side of the main solenoid valves and relay R8,
de-energizing R7 and the spark generator.
4. If the pilot flame isn’t sensed, the FSM de-energizes the PV
terminal and waits 5 minutes before initiating the second ignition
trial. The blower(s), pump(s) and optional power venter will
remain on during this time.
5. On CSD-1 equipped units the blower(s) and optional power
venter will shut down and the boiler/water heater will lock if
the second ignition trial fails. The unit must then be manually
reset by depressing the reset button on the left jacket panel.
6. On non-CSD-1 equipped units the FSM will wait 10 minutes
after the second unsuccessful ignition attempt then begin the
ignition process described in step 3 above. The FSM will continue
to cycle the unit through steps 3, 4 and 6 until the unit lights
or the demand for heat is removed.
Main Burner
Once the pilot is proven, the FSM sends 24VAC to its MV terminal
energizing the safety and low-fire side of the main solenoid valves.
Normal Operation
• Staging is controlled by the return water aquastat. Relays R2
and R2R are energized by the return water aquastat when more
heat input is required. The hi-speed windings of the blower(s)
are energized.
• Relay R9 is energized when the hi-fire pressure switch senses
adequate air pressure to sustain hi-fire combustion. R9 energizes
the hi-fire side of the main solenoid valve.
• Stage 1 will operate first and last.
For a change from stage 1 to 2, a 30 second time delay
is provided in the pressure switch switching circuit.
The time delay TD6 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. When the demand for heat is satisfied the low operator switch
will open, de-energizing relays R2, R2R, R8, R9, TD1, TD3,
TD4, TD6, the FSM, and the pilot, main and safety solenoid
valves. The pilot and main flames are extinguished.
2. The blower delay timer TD3 starts the 80 second post-purge
timing. The blower(s) shut(s) off when TD3 times out.
3. The pump delay timer TD4 starts the post-purge timing. The
pump(s) remain on for 0.1 to 10 minutes then shut(s) off when
TD4 times out.
High Limit, Low Water Flow, Low Gas Pressure, High Gas
Pressure, Power Venter Interlock Faults
1. Electrical power to the gas valves, blower(s) and power venter
will be interrupted if any safety is tripped.
2. The manual reset high limit can be reset by depressing the reset
button on the left jacket panel.
Low Air (Blocked Flue/Air Inlet)
• The pressure switches will monitor blower airflow.
• Air monitoring will begin at pre-purge. If a low air condition is
present, power will not be supplied to the FSM. The blower(s)
will remain on.
