LAARS Mascot ll LMC - Install and Operating Manual - Manual (Page 29)

Mascot II Boilers and Water Heaters Page 27
8.2 Ignition Control- Sequence of Events
1. Call for heat
2. Safety chain check
3. Fan starts.
4. Prepurge timer is started.
5. Pre ignition time of 2 seconds to check the flame
sensor operation and status.
6. Trial for ignition period, 4 seconds. The direct
spark ignition switches to constant spark for three
seconds, during which time the gas valve is open.
For the last second of the ignition period direct
spark is de-energized and the flame sensor checks
for established flame. If flame is sensed the control
enters "Run" to satisfy the demand. If flame is
not established the control enters a retry, starting
from step 2. If flame has not been established in
the appropriate number of retries the control will
lockout with a 109 error code.
7. Call for heat complete
8. Gas valve off
9. Fan and pump over run times active to purge the
system
The sequence is the same for DHW or Central
Heat modes. Upon a call for Central Heat, the 3-way
valve will shift position, allowing boiler water to enter
the building's heating loop.
8.3 Modulation Control
The control uses a PID algorithm to adjust
the firing rate of the boiler as the control point is
approached. The goal of the control is to operate
at a minimum firing rate to match the load on the
appliance. The burner modulates to achieve the setpoint
temperature, away from the actual off point.
8.4 Pump Control
The boiler pump is active anytime there is a call
for heat applied to the control. When there is a central
heat call supplied the system pump relay is active. If
there is a DHW call supplied while the central heat
call is active the system pump turns off. This happens
because of domestic hot water priority, which forces the
control to satisfy the domestic water demand prior to the
hydronic demand. When the last heat demand is satisfied
the boiler pump enters an overrun time.
8.5 High Limit
The control uses a dual thermistor sensor to
monitor the Mascot II'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
Mascot II to prevent the high limit from tripping. The
high limit setpoint is not adjustable.
8.6 Stack Temperature
The stack temperature is a dual thermistor sensor
and is limit rated. The control compares each of the
temperature readings to determine accuracy. The stack
sensor is used as a limiting feature to avoid excessive
temperatures in the venting.
8.7 Domestic Hot Water Temperature
The domestic hot water temperature sensor is used
to control DHW temperature. The DHW setpoint can be
adjusted through the USER menu structure.
DHW setpoint is displayed during DHW mode.
For LMH model, an aquastat will be used in lieu of a
sensor to control temperature of an indirect tank.
8.8 Lead Lag / Cascading
Lead Lag/Cascading allows multiple boilers to be
connected together and controlled from one common
sensor input. Up to 8 boilers can be connected together
in a single system. To setup Lead/Lag or cascading
operation there are several settings in the "setup"
menu structure that must be adjusted for the specific
installation, each is covered in the following sections.
8.8.1 Lead Lag Setpoint
The lead lag setpoint is set from the "user"
menu using the "LL" variable. This is the temperature
the boiler is attempting to maintain at the system
sensor. This setting doesn't control the boiler outlet
temperature, so the water temperature at the boiler
outlet may be much hotter than the system temperature
setpoint. Adjust the LL setpoint to the desired operating
temperature of the system.
8.8.2 Lead Lag Master/Slave Selection
In the SETUP menu structure, the "LL" menu
allows the lead lag system to be turned on and the boiler
to be configured as a master or slave control. In each
lead lag system there can only be one master control, so
proper selection is important to avoid operating issues.
To set the boiler to lead lag "master" operation the LL
menu should be set to "LDR". To set the boiler to slave,
"SLA" should be selected.
8.8.3 Lead Lag Address
The Lead Lag address must be set for each boiler
connected to the lead lag system. Each boiler must
have a unique address selected for the system to work
properly. Typically, the lead or master boiler should be
set to address one and the remaining boilers should be
set to values 2–8 depending upon how many boilers are
installed in the system.
8.8.4 Lead Lag Hysteresis
The lead lag system uses a hysteresis value set
in the setup menu, called, "HS". The hysteresis and
setpoint values control the on and off points of the
boiler. If the lead lag setpoint is adjusted to 120°F with
a hysteresis value of 5°F the boiler will turn off when
the water temperature reaches 125°F and will turn back