LCD Series Finned Copper Tube Gas Boilers & Water Heaters – Boiler Manual
26
BOILER/WATER HEATER OPERATION
Staging Operation
The LCD boiler/water heater series is separated into on/off and
2-stage units depending on the model selected. The 400 model has
on/off staging, while the 600 through 2300 models have a two
stage option. Input staging is controlled from an aquastat controller
that signals the relays to select the blower and gas valve modes.The
boiler will not operate without the outdoor sensor installed. Table
13 identifies the stages and firing modes associated with the standard
single stage units. Table 14 identifies the stages and firing modes
associated with the two stage option.
Table 13 Firing modes (400-2300)
Stage
Firing Mode
Off
Off
1
On
Table 14 Firing modes (600-2300)
Stage
Firing Mode
Off
Off
1
Low Fire
2
High Fire
The outlet water temperature is automatically controlled by the
aquastat. The optional staging function is controlled by a return
water aquastat. The return water aquastat utilizes inputs from the
inlet water temperature sensors or optional tank sensors to stage
the boiler/water heater as required.
Pressure Switch Settings
Differential pressure switches are provided in the LCD to shut down
gas flow under a blocked flue or inlet condition. A single pressure
switch is used on the standard models. One low fire and one high
fire pressure switch is used when the two-stage option is employed.
The low fire pressure switch serves to shut down gas flow if there
is a blocked flue or inlet condition during low fire operation. Similarly,
the high fire switches will shut down gas flow if there is a blocked
flue or inlet condition during high fire operation.
The differential
pressure is taken between the air plenum and the pressure
inside one of the main burners.
Pressure taps are provided in the control compartment for taking
the differential pressure readings, Figure 17. Table 15 lists the
differential pressure settings for all of the models.
Figure 17
Pressure switch tap(s)
Table 15 Differential pressure settings (all units)
Model
Differential Pressure
Requirement at High Fire
(All Units)
Inches WC
mm WC
400
0.7 ± 0.8
17.8 ± 20.3
600-2300
1.0 ± 1.1
25.4 ± 27.9
On all units, the pressure switch(es) will interrupt power to the
control module under a blocked flue or inlet condition. This will
cause the pilot and main gas valves to close. Tables 16 and 17 identify
how pressure switch control changes during boiler/water heater
staging. Tables 18 and 19 identify the control actions if a low air
condition occurs at any stage.
Table 16 Pressure switch control, 400
Stage
Pressure Switch Mode
Off
Off
1
High Fire
Table 17 Pressure switch control, 600-2300
Stage
Pressure Switch Mode
Off
Off
1
Low Fire
2
High Fire
