LAARS Mighty Therm2 MT2P (Sizes 500–2000 MBTU/h) - Install and Operating Manual - Manual (Page 18)

LAARS Heating Systems Page 18
once if optional lockout ignition is used.) When the
call for heat is satisfied, the gas valves(s) close and the
blowers continues to run for 30 seconds.
The pump will continue to run for 0.1 to 10
minutes, depending on what the pump time delay
has been set to. Mighty Therm2 sizes 1000-2000
have two ignition controls that control the individual
stages. If one ignition control should fail for any
reason, the remaining module can operate its burners
independently. (Note that if a single blower is disabled
on units 1250-2000, the other fan will continue to
operate and safely allow the boiler to run with a single
stage.)
6.2 Filling the Heater System
1. Ensure the system is fully connected, filled with
water and all valves are open.
2. Start up heater according to the procedure in this
manual. Operate the entire system for one (1)
hour.
3. After placing the unit in operation, the ignition
system safety shutoff device must be tested. First,
shut off the manual gas valve, and call the unit
for heat. After the pre-purge and ignitor heat-up
time, the main gas terminals will be energized,
attempting to light, for four (4) seconds, and then
will de-energize. The unit will go into lockout
mode. Second, turn the power off and then on
again, push the reset button (optional Ignition
Module only), open the manual gas valve and
allow the unit to light. While the unit is operating,
close the manual gas valve and ensure that power
to the main gas valve no longer exists.
4. Check the entire system for leaks.
Caution
Protect the heater from low pH water if an “acid start
up” or similar technique is used. Corrosion of the
heater and heat exchanger due to low pH water is
not covered under the limited warranty. The water
must be neutralized to normal pH levels before filling
the heater and starting up the system.
Important: The installer is responsible for identifying to
the owner/operator the location of all emergency shutoff
devices.
WARNING
Do not use this appliance if any part has been under
water. Immediately call a qualified service technician
to inspect the appliance and to replace any part of
the control system and any gas control that may
have been under water.
The other limit control limits the temperature of
the discharge from the heat exchanger to a maximum of
190°F. This limit should be set to a minimum of 175°F.
To set the limit controls, remove the control panel cover
and pull the control panel out to gain access. Appliances
with reversed heat exchangers have the limit controls
relocated to the left side of the appliance. The left
access door must be removed to gain access to the limit
controls on these appliances.
SECTION 6.
Operating Instructions
6.1 Sequence of Operation
Upon initiation of the main power switch, 120V
will be sent to multiple items. Among these are the
open contact fan relays, open contact ignitor relay, open
contact pump relay, ignition control module(s) and open
contact lock out indicators (the optional alarm package
uses this). In addition to these, 24V will travel through
the optional gas pressure switches and optional auto
reset high limit and boiler control relays. The 24V will
then travel through the block flue switch and the manual
reset high limit to the temperature controller.
Upon a call for heat from the MT2’s internal
control or an external staging control, 24V travels
through the field interlock (if closed) and then to the
ignition control(s) “T-stat” terminal (500-750 models
are equipped with one ignition control and models
1000-2000 are equipped with two ignition controls).
When “T-stat” on an ignition control is energized,
its fan will energize and the ignition control will seek
signal from the “pressure circuit”. The pressure circuits
consist of the flow switch and proof of fan.
Models 500-1000 calls for fan, fan prove, initiate
pump then prove flow, after which “pressure circuit”
has been satisfied.
Models 1250-2000 calls for pump, proof of
flow, initiate fan then prove fan, after which “pressure
circuit” has been satisfied. The fan prove will only
occur for the active stage that has been called.
When pressure circuit has been satisfied, proving
combustion air and adequate water flow, the hot surface
igniter will initiate. The ignition control checks that the
igniter current reached a predetermined level then will
dwell momentarily. When dwell time is complete the
gas valve will open.
After a 4-second trial for ignition, the igniter
switches off. Unless a flame is detected by the flame
sensor (a minimum value of 0.4µA), the gas valve
will close and The ignition module will either attempt
ignition again (up to three times) or will lock out if the
optional lockout ignition module is used.
If flame is sensed, the burner will continue to fire
as long as there is a call for heat and adequate flame
signal. If there is a subsequent loss of flame signal, the
burner will attempt re-ignition up to three times (only