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Mode 2 – Permanent Demand and Outdoor Reset:
Mode 2 operates much like Mode 1 except that no
thermostat contact closure is required between
terminals #1 & #2 in the electrical panel to operate
the boiler. The boiler will attempt to constantly
maintain the target temperature calculate by the
control. The factory defaults for this mode are the
same as in Mode 1. Details for outdoor reset are
covered in subsection 3 below.

A contact closure between terminals #1 & #2 will
result in a target temperature setback of 18°F. This
feature may be used in conjunction with a timer or
switch for unoccupied setback periods.

Mode 3 – Permanent Demand: Mode 3 also operates
without a thermostat closure although it targets a fixed
temperature selected from the User Menu.

Based on

the Federal regulations this mode cannot be used for
space heating unless the boiler is the managing boiler
of a multiple boiler cascade system having a total
input of 300,000 btu/hr or greater.

Mode 4 – 0-10 VDC Input to Modulate Setpoint: The
optional PFA-1 Interface Adapter Kit (54271) allows
the control to accept an analog 0-10 VDC external
signal which changes the target supply temperature. A
minimum input of 2 VDC is required to activate the
boiler. Voltage inputs between 2 &10 VDC will
proportionally adjust the boiler outlet temperature
target.

This mode is commonly used in conjunction with a
Building Management System (BMS) to control the
boiler outlet target based on the building
requirements.

Mode 5 – 0-10 VDC Input to Modulate Firing Rate: In
this mode, the optional PFA-1 Interface Adapter Kit
(54271) accepts an analog 0-10 VDC external signal
to directly control the boiler input rate. Similar to
Mode 4, a minimum input of 2 VDC is required to
activate the boiler. At 2 volts the display will show 1%
of modulation which is equivalent to the minimum
input. 10 VDC will cause the modulation to increase
to 100% of input. The input rate between these two
points is proportional to the signal. Note that the
boiler high limit is set a 210°F and will cause a lockout
if this temperature is reached.

Mode 6 – Hydro-Air Units: This mode is specifically
designed for boiler supplying hot water to a hot water
coil in a forced air heating system using fixed supply
target and activated by a thermostat contact closure
between terminals #1 & #2 in the electrical panel.

Based on the Federal regulations this mode cannot be
used for space heating unless the boiler is the
managing boiler of a multiple boiler cascade system
having a total input of 300,000 btu/hr or greater.

Using CH Mode 1 with the Hydro-Air presets
described below in subsection 3 is likely a better
option for this operation.

Mode 7 – Internal Reset: This is the default setting for
the CH Mode. In this mode, the control calculates the
target supply (outlet) water temperature based on the
frequency and duration of central heat (CH) demand
from the thermostat contact closure between terminals
#1 & #2 in the electrical panel.

• As the thermostat demands become longer

and more frequent, which indicates a larger
heating load, the boiler supply target
temperature will increase.

• As the thermostat demands become shorter and

less frequent, indicating a smaller heating load,
the boiler supply target temperature will decrease.

The rate of temperature change can be adjusted to
enhance the efficiency and comfort level. Figure 8.2
shows how the boiler supply target temperature
increases and decreases over time depending on
whether or not there is a call for heat. The graph
shows the default values for all of the settings which
affect CH Mode 7. Table 8.7 shows these values.

The target boiler water temperature will not increase
beyond the Boiler Design Temperature or decrease
below the Mild Weather Boiler Temperature.

BOILER CONTROL: INTERNAL WIRING & OPERATION

Table 8.7: CH Mode 7 Menu Settings

Menu Setting

Minimum

Default

Maximum

Increment (Temp. Increase)

0.9°F

1.8°F

36.0°F

Decrement (Temp. Decrease)