LAARS Mascot LX MLXC 175 MBH - Install and Operating Manual - Manual (Page 49)

Mascot LX Boilers and Water Heaters Page 45
SECTION 12.
Troubleshooting
12.1 Sequence of Operation
Mascot LX is a cold start appliance that should start
only on a call for heat from a tank aquastat, room
thermostat, zone valve end switch or other space
temperature control device (flow switch for DHW).
1. Upon a call for heat: (a) the internal pump and
system pump will start; (b) the blower will begin a
short pre-purge.
2. Following the prepurge cycle the direct spark
ignition will spark and will begin a 4 second
trial for ignition. The unit is allowed one or three
ignition retries.
3. The gas valve will then be energized and a reduced
45% rate ignition will occur. The unit will remain
in the reduced rate start-up period for
ten (10) seconds.
4. After the reduced rate start time is over, the
unit will be in normal operation. Firing rate
will modulate based on the heating load via the
temperature controller settings and readings.
5. When the call for heat is complete, or the unit
reaches its setpoint temperature, the gas valve will
close, and the fan will continue to run for its post-
purge. If a pump delay time is used, the pump will
continue to run for the specified amount of time
(adjustable from 0.1 to 10 minutes).
12.2 Short Cycling
Because Mascot LX is a modulating boiler, and its
input will decrease when there is a reduction in 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
or piping layout. When in DHW mode under low load
conditions, the boiler will normally cycle more often,
but should not cycle frequently during call for central
heating.