LAARS NeoTherm NTV (Sizes 150–850 MBTU/h) - Install and Operating Manual - Manual (Page 63)

Page 59 N eo T herm Boilers and Water heaters
11.5 Anti-Short-Cycle (ASC)
Because the NeoTherm unit is a modulating boiler, and its
input will decrease when there is a reduction in the heating
load, short cycling is greatly reduced. If the heating load
drops below the minimum input of the boiler for an extended
period, the boiler will have a tendency to short cycle. This can
be a symptom of improper control strategy or setpoints, or a
load distribution problem. The controller in the NeoTherm
unit includes an anti-short cycle (ASC) function. The timer
for the ASC can be set to delay the boiler start for a specified
time after a call for heat is completed.
11.6 Temperature Sensors
High Limit Sensor -
The control uses a dual thermistor sensor to monitor the
Neotherm’s maximum temperature. The high limit sensor
is installed in the outlet water. A dual thermistor sensor is
used, so that the two temperatures can be monitored and
compared to confirm accuracy. The control will automatically
reduce the firing of the NeoTherm to prevent the high limit
from tripping. The high limit setpoint is factory set at 195°.
However, if desired you can set a lower limit using the
Adjustable High Limit function available from the Quick
Start menu.
Outlet Water Temperature -
The outlet water temperature is sensed by a dual thermistor
sensor, and is limit-rated. The control compares the two
temperature readings to determine accuracy. The outlet
sensor is used as the primary control point for high limit,
temperature operation, and modulation.
Inlet Water Temperature -
The inlet water temperature uses a single thermistor sensor.
The heat exchanger temperature rise (delta T) is calculated
using the inputs from the outlet and inlet sensor temperatures.
Stack Limit -
The stack temperature is sensed by a dual thermistor
sensor, and is limit-rated. The control compares both of the
temperature readings to determine accuracy. The stack sensor
is used as a limiting feature to avoid excessive temperatures
in the vent.
11.7 Diagnostics
Use the Diagnostics to check the status of the sensors and the
digital inputs and outputs. The system also records a history
of lockouts and alarms.
Analog Sensors -
You can use this display to check on operating temperatures,
fan speed, firing rate, etc. (The word “analog” refers to values
that can change continuously between zero and a higher
value.) The values shown here are “Read Only” – you can’t
change them from this display.
Digital Input/Output -
This display shows whether different functions, inputs and
outputs are either on or off. The functions listed here include
pumps, valves, alarms, etc. The values shown here are “Read
Only” – you can’t change them from this display.
History -
The system records the most recent lockouts or alerts. (If
there is a current lockout or alert, a note about this will also
appear at the bottom of the Home screen.)
• A “lockout” is a condition that will prevent the unit from
starting or running.
• An “alert” indicates a condition that is not normal. If it
continues, the control system might move to a “lockout,” or
the problem might be corrected.
11.8 Error Codes
See Appendix B.