LCD Series Finned Copper Tube Gas Boilers & Water Heaters – Boiler Manual
27
Table 18 Low air condition action, 400-2300
Stage
Control Action
1
No Power to Flame Sense Module
Table 19 Low air condition action, 600-2300
Stage
Control Action
1
No Power to Flame Sense Module
2
No Power to Flame Sense Module
OPERATION SEQUENCE, ON/OFF
400 THROUGH 2300
Refer to the wiring diagram included with the unit
for further control system info.
POWER ON:
Demand for Heat:
1. The 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 interlocks before
starting pre-purge. The unit will not start if any switch is open.
Prepurge:
1. Blower delay timer TD3 energizes the high speed windings of
the blower(s).
2. Air pressure in the combustion chamber is sensed. If the air
pressure is sufficient, 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 main solenoid valves and relay R8, de-energizing relay 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 MV terminal on the FSM is energized
sending 24VAC to the safety and main solenoid valves.
Normal Operation
On single stage units the blowers and gas valves operate at one
input.
Demand Satisfied:
1. When the demand for heat is satisfied the operator switch will
open, de-energizing relay R8, TD1, TD3, TD4, 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 optional 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 switch 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.
