LAARS NeoTherm LC NTV1700 - Install and Operating Manual - Manual (Page 50)

LAARS Heating Systems Page 46
Fig. 50 – Lead/Lag Activity in a Multi-Boiler
System
Low demand -
The first burner* in
sequence fires at
less than 65%
First
burner*
Second
burner*
Third
burner*
Fourth
burner*
Boiler X Boiler Y
Demand increases -
Once the first burner
reaches 50%,
the second burner*
switches on, and
both modulate
together between 29%
and 65%
Demand increases -
Once the first two
burners reach 65%,
the third burner*
switches on, and all
three modulate together
between 29% and 65%
Nearing max. demand -
The fourth burner* is
active. Once all four
reach 65%, all are
allowed to go over
65%
* - The Lead/Lag controller will change the firing order of the
burners, based on the run time of each burner.
9.1.3 NTH Lead/Lag with Indirect
Domestic Hot Water
So far, we have been describing a system which
handles the Central Heat function only. There are
several ways the Domestic Hot Water can be set up
on a Lead/Lag system. For a detailed description,
see Section 9.5.
9.2 Connection Terminals
Figure 51 shows some of the connection terminals
on the circuit board inside the cabinet.
WARNING
Before connecting or disconnecting any wiring
inside a boiler, be absolutely sure to turn off all
electrical power to the unit. Failure to do this
could result in property damage, serious injury or
death.
9.3 NeoTherm LC System
Configurations
NeoTherm LC’s can be installed in many different
arrangements. The steps in the installation will be
different, depending on the number of boilers in the
system, the venting arrangements, the control signals
used, and so on. In this section, we will list the steps
necessary to do the most common installations.
1. Table 12 lists most of the common
configurations for NeoTherm LC systems.
Look through the table until you find a line
that exactly describes your system. Make a
note of the system number shown in the left
column.
2. Following the table, look up the specific
installation jobs for your system in Section
9.4. The jobs are identified using letters (Job
A through Job P).
If you are not familiar with the NeoTherm
LC’s or the Lead/Lag control system, you
may want to review the information in Section
9.1. This may be helpful as you read the
installation instructions which follow.