Installation, Operation and Maintenance Instructions User guide

MagnaTherm Boilers and Water Heaters
Page 51
Figure 27. Lead / Lag Operation, 3 or more boilers
Low demand -
The first boiler in
sequence fires at
less than 65%
1 2 3 4
Demand increases -
Once the first boiler
reaches 50%,
the second boiler
switches on, and
both modulate
together between 29%
and 65%
Demand increases -
Once the first two
boilers reach 65%,
the third boiler
switches on, and all
boilers modulate together
between 29% and 65%. This continues as demand increases.
5 6 7 8
Nearing max. demand -
The last boiler becomes
active. Once all boilers
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.
Number of boilers
installed
Base load value
1 NA
2 65%
3 50%
4 35%
5 35%
6 35%
7 35%
8 35%
Table 15. Base Load Settings
• When the Run sequence is initiated, the
boiler with the least amount of runtime
will re.
• If the heating demand increases so that
the ring rate of that rst boiler rises to
your boiler congurations Base Load
Value (see Table 15), the next boiler in
the sequence will start up and begin ring
at 20 to 35% fan speed (depending on
your conguration). After this, the entire
conguration of boilers will modulate
up or down together, in reaction to the
changes in demand.
See Figure 25 and Figure 27
Control Settings for Lead/Lag System -
Part 1
1. Power up all of the boilers in the system.
2. In an installation with several boilers, you
must give each boiler a different name,
sot that the controller of the Lead/Lag Master can
communicate with the other units. All of the units
come from the factory with a Modbus address of “1,”
so you will need to change some of these addresses.
On each unit, go to the screen for “System ID and
Access,” and enter a unique name.
3. The unit operating as the Lead/Lag Master must be
‘Master Enabled’ rst and then set up address “1,” and
the other boilers should each be ‘Slave Enabled’ and
have unique Modbus address numbers typically 2 thru
X (total number of boilers)
On the boilers, touch the controller Icon on the Home
Screen.