Mighty Therm
2
(200, 300, 400)
Page 27
LEDs State Description
1. Power
2. Heat – On = call for heat; Flashes for Boiler
sensor error
3. DHW – On = call for DHW; Flashes for
outdoor sensor error
4. WWSD – On = Outdoor Reset AND WWSD
Active AND control in WWSD; Flashes for outdoor
sensor error, operation continues with fixed boiler
target of 140°F.
When a call for HEAT and/or DHW is present
the pump contact (5A max) will be energized. Post
purge can be selected via dip switch #5, Pump Post
Purge Inactive (Off) /Active 3 min. (On). In the On
position the pump will continue to run for 3 min after
the last call has been satisfied. When the dip switch is
Off there is no post purge of the pump, the pump turns
off immediately after the last call is removed. Laars
strongly recommends using a pump post purge. During
WWSD and a call for HEAT is present the pump will
remain off.
Pump Exercising
The control exercises the
boiler pump every 3 days of inactivity. While the
control is exercising the pump all LEDs will turn off
and the power LED will flash for 10 seconds.
Staging (where applicable – factory setting
):
Dip switch #1 is used to select the number of stages:
2-Stage (Off) / Single Stage (On).
For 2-stage operation, the first stage is cycled
on Proportional error and the second stage is cycled
based on PI according to a fixed algorithm. No user
adjustment is necessary.
Note: All stages are turned off when the water
outlet temperature reaches the Maximum setting
that is elected via dip switch #4, Boiler Maximum
210°F (Off) / 190°F (On). Commercial boilers have
dip switch #2 set for ‘Off’ to allow setpoint control.
Utilize dial to set desired outlet temp.
NOTE:
This boiler is equipped with a feature that saves
energy by reducing the boiler water temperature as
the heating load decreases. This feature is equipped
with an override which is provided primarily to permit
the use of an external energy management system
that serves the same function. THIS OVERRIDE
MUST NOT BE USED UNLESS AT LEAST ONE OF
THE FOLLOWING CONDITIONS IS TRUE:
• An external energy management system is
installed that reduces the boiler water temperature
as the heating load decreases.
• This boiler is not used for any space heating.
• This boiler is part of a modular or multiple boiler
system having a total input of 300,000 BTU/hr or
greater.
• This boiler equipped with a tankless coil.
Auto Boiler Target Setpoint: Space Heating:
The boiler target temperature is automatically
determined from Space Heating and DHW
requirements. Space heating is based on outdoor reset.
When both a Heat Call and a DHW Call are present
at the same time, the control operates to provide the
higher boiler target temperature.
Heating Curve (Outdoor Temperature Reset)
The control uses a linear heating curve to calculate
a target setpoint. The following data are used
to calculate the target setpoint from the outdoor
temperature.
1. The heating curve or reset ratio (RR) is set by
the potentiometer with a range of 0.4 to 3.6.
2. The room temperature is fixed at 70 deg F.
3. Boiler target = 70 deg F + RR x (70 deg F -
outdoor temp)
Outdoor
Heating Curve=Reset Ratio (RR)=
Temp F
1.0
2.0
3.0
Boiler Target F
-30
170
210
210
-20
160
-10
150
0
140
10
130
190
20
130
170
30
150
190
40
130
160
50
130
60
70
WWSD OFF
Boiler Target Temperature Calculation:
Boiler Target = 70 deg F +RR x (70–Outdoor
Temp)
DHW Operation
The boiler target for DHW
calls is fixed at 180 deg F.
Note: There is no control of a DHW pump, so the
boiler pump runs with the call for DHW.
Limiting
The boiler target is limited to a
minimum and a maximum target to ensure that the
water temperature does not exceed the limits.
1. Target Min
- The boiler target minimum is
the point at which the stages will start to turn on to
maintain a minimum water temperature. The Boiler
Minimum water temperature is 130 deg F, regardless
of other calculated targets. To ensure that the water
temperature is greater than the Boiler Minimum water
temperature the target is increased to allow the stages
to cycle on by the Boiler Minimum water temperature,
Boiler Minimum target is set to Boiler M
