LAARS Mighty Stack MS-080 (Sizes 199, 300, 399) - Install and Operating Manual - Manual (Page 21)

Mighty Stack Page 21
Figure 8. Logic Diagram, ON/OFF Water Heater.
control (F1 and F2). The ignition control will remain
in this fault mode, with the blower off. If the power to
PSW is removed while there is still a call for heat, the
ignition sequence will start again, but the main valves
will not be energized until PSW sees power during the
ignition sequence.
At the start of an ignition sequence, the control
sends the combustion blower output (F1 and F2). If
the control does not see power at PSW for more than
30 seconds, the control will remain in this fault mode,
with the blower on. If proper airflow is later detected
on PSW, the control begins a pre-purge and a normal
trial for ignition.
If the PSW signal is lost while the Mighty Stack
is firing, the control will immediately de-energize the
gas valve terminal (MV). The blower will remain on
for the post-purge period (45 seconds), and the control
will continue to monitor the PSW input. If the signal
is detected during the post-purge period, a normal trial
for ignition will begin, starting with the 15-second
pre-purge. If the signal is not detected during the post-
purge, the control will lockout with the blower off.
6.6 Operating the Burner and Set-Up
6.6.1 Set-Up for 0 to 2500 Feet Altitude
The setup must be checked before the unit is put in
operation. Problems such as failure to start, rough igni-
tion, strong exhaust odors, etc. can be due to improper
setup. Damage to the Mighty Stack resulting from
improper setup is not covered by the limited warranty.
1. Using this manual, make sure the installation
is complete and fully in compliance with the
instructions.
2. Determine that the appliance and system are
filled with water and all air has been bled from
both. Open all valves.
3. Observe all warnings on the Operating
Instructions label and turn on gas and electrical
power to appliance.
4. Switch on the appliance power switch located on
the right side of the unit.
5. The Mighty Stack will enter the start sequence,
as long as the unit is being called for heat. The
blower and pump come on for pre-purge, then
the ignitor warm-up sequence starts and after
the ignitor warm-up is complete and all safety
devices are verified, the gas valves open. If
ignition doesn’t occur, check that there is proper
gas supply. Wait 5 minutes and start the unit
again. During initial start up, air in the gas line
may cause the Mighty Stack to "lock out" during
the first few trials for ignition. If the ignition
control locks out, reset by cycling the power off
and on using the main power switch on the right
side of the cabinet.
6. When the unit is running, the supply gas pressure
must be checked. Inlet gas pressure must not
exceed 13 in. w.c. (3.2 kPa). The minimum inlet
gas pressure is 5 in. w.c. (1.2 kPa) and 8 in. w.c.
(2 kPa) for LP.
7. Once the inlet gas pressure is verified, the outlet
gas pressure (manifold gas pressure) must be
checked, and adjusted, if necessary. The manifold
gas pressure must be 3.0 in. w.c. (0.62 kPa) for
natural gas and 9.0 in. w.c. (2.2 kPa) for LP.
8. Complete the setup by checking the CO
2
at the
outlet of the unit. The CO
2
should be 8% for
natural gas, or 9.2% for LP.