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CONTROL OPERATION
Initial Start Up
When electrical power is applied to AT boiler the control
displays rmware revision code. It will then revert to mode
it was in prior to power loss (factory setting is OFF mode).
Pressing MODE/PWR button for 2 seconds, unit will enter
ON mode. Pressing MODE/PWR button again for 2 seconds
will return unit to OFF mode. Once in ON mode the control
automatically begins a Dry Fire Test (if DFt is set to Y in the
conguration) where pump is energized and rst element
is pulsed. (see Dry Fire Test Mode). Dry Fire Test is only
initiated after power loss. To by-pass Dry Fire Test Mode
and enter heating mode, press ▲up and ▼down arrow
buttons for 2 seconds.
Two Temperature Operation
AT boiler is designed to control two loads with independent
temperature control such as a comfort heating zone
(CHS) and indirect domestic hot water tank (DHS). Other
applications include in-oor radiant system with n tube
baseboard system.
Setting Water Temperature
To set boiler water temperature, place boiler in on mode
and then select temperature setting mode by pressing
MODE/PWR button. Use ▲up or ▼down arrow buttons to
set temperatures for comfort heating “CHS”, domestic hot
water setting “dHS” and differential setting “dFS”.
NOTICE
Setting for CHS cannot exceed setting for DHW. Setting
for DHW cannot be set below setting for CHS.
Heating Operation Sequence
To begin heating sequence control board must be “On” for
boiler operation. All safety inputs must be closed (HL, LWC,
FLO) as well as Load Management Control (LMC) terminals.
Setpoint temperature for either CHS or dHS must be above
current water temperature.
To start boiler heating sequence the thermostat or pump
end switch will close the connection between terminals
[Comfort heat - R & W (T & T)] or [Domestic hot water -
DHW_T&T] on the control. Pump relay energizes for 30
seconds prior to electric elements while a check of safety
circuit and water temperature is conducted. (Note Flow and
LWCO circuits check is conducted after the pump starts,
since water ow and water level are dependent on pump
being energized). If heating load is satised by residual
heat in the boiler during 30 second pre-purge period the
elements will not energize. Heating element(s) will begin
to energize after 30s pre-purge is complete.
LED’s for heating elements, pump status and heat call will
illuminate as each is energized. If safety circuit is open
elements will not energize and error code is displayed.
During heating operation the safety circuit is monitored.
If no faults exist the rst element will energize and rate of
water temperature rise is calculated.
Control will energize elements in sequence based on
temperature rise of water and target time of 5 minutes
to reach setpoint. Minimum on an off times apply to each
element.
When water temperature approaches setpoint temperature
heating elements will de-energize to prevent water
temperature from exceeding setpoint temperature. When
water temperature reaches set point all remaining heating
elements will de-energize. Control will then cycle elements
on and off to maintain set point temperature. At start
of each subsequent heating cycle the lead element to
energize will rotate to allow for even duty cycle time over
all elements.
Pump will remain energized while there is call for heat
(TT or DHW-TT closed). When call for heat is satised unit
enters post purge period. Pump shall remain energized
for 3 minutes starting at point in which last element de-
energized.
Rate which elements energize and de-energize to maintain
water temperature can be adjusted. Differential setting
is used to determine point which heating elements are
energized or de-energized. Increasing differential setting
will de-energize heating elements sooner and reduce
potential for temperature overshoot. A larger differential
will also reduce cycles per hour of the boiler.
Decreasing differential setting will keep heating elements
on longer and allows for tighter set point control increasing
potential for temperature overshoot. A small differential
also increases boiler cycles per hour.
Starting point for differential setting is 10°F (5.5°C).
Depending on application, boiler size, number of heating
zones and whether or not there is domestic hot water
application, differential setting can be adjusted to
accommodate the installation.
Dry Fire Test
Dry Fire is not a substitute for a low water cutoff
sensor control.
Dry Fire Test detects presence or lack of water in the boiler
and prevent elements from energizing if dry condition exists.
Dry Fire Test Mode is initiated following power outage and
can take from 5 to 10 minutes to complete. Boiler must be
ON and conguration setting for dFt must be set to Y. During
Dry Fire Test pump is energized and rst heating element is
pulsed while temperature sensor is monitored to determine
if water is present in the boiler. If failure occurs, “DFF” is
displayed and a re-try takes place. After three consecutive
failures an audible alarm will sound and pump will stop.
Power must be removed and dry condition corrected to clear
fault code.
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