Laars MASCOT LX, Service Manual

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Mascot LX Service Manual
Appendix 2 - Ignition and Firing Sequence
App2
This is the basic operating sequence of the boiler whether there is a
hydronic or domestic hot water call for heat.
1. The unit receives a call for heat.
2. The boiler pump and the system pump start. Once the fan reaches
operating speed, the blower begins a pre-purge for 10 seconds.
3. After the pre-purge, the direct spark and gas valve activate, and the
unit starts a four-second trial for ignition.
4. The unit fires and runs at a reduced rate of 45% for 10 seconds.
5. After the reduced rate time has ended, the flame signal is compared
with a pre-set standard. If the flame is adequate, the unit goes to
normal operation. It will modulate based on the system load and the
control setpoints.
6. When the call for heat ends, or the set point is reached, the gas
valve closes, and the flame goes out.
7. The fan continues to run in post-purge for 11 seconds.