Install Instructions

Page 53
NEOTHERM Residential Boilers
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 specied
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 conrm accuracy. The control will automatically
reduce the ring 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, ring 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. on page 66