LAARS Mini-Therm JVS (Sizes 50-225) - Install and Operating Manual - Manual (Page 29)

Page 29
8.E Operating Temperature Controls
Note: The Temperature Controllers, the Dip switch
panel, and the LED panel can be found under the
Control Access Panel after removing the bolts.
Two temperature controls are now standard on all
JVS and JVH boilers.
1. The primary temperature controller maintains
all normal heating operations.
2. A secondary, mechanical high-limit aquastat
provides safe shutdown, should the primary
controller fail.
Important: If the secondary controller (See Figure
18A and Figure 18B) dial is set below 220F, it may
inhibit proper operation of the primary controller.
Prior to calling for technical support, please ensure
high limit control is set for at least 220F.
Figure 18B. Secondary, mechanical high-limit
aquastat
Pump Operation. When a call for HEAT and/
or DHW is present the boiler pump will turn on. 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 #1 is used to select the number of stages: 2-Stage
(Off) / Single Stage (On).
Note: Use of 2-Stage operation may reduce
efficiency.
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).
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.
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
Reset Ratio Calculation:
Boiler Target = 70 + RR *(70 - Actual Outdoor)
Table 9
1.
2.
Control Access
Panel
Figure 18A.