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Page 76
Fig. 113 – Lead/Lag Master Configuration
Entries on this screen allow you to set the CH
setpoint and DHW setpoint.
4.
Press the button for Advanced Settings. This
leads to a "ring" of related screens, and you
can scroll through the list by pressing one of
the left- or right-arrow symbols. Press the left-
arrow or right-arrow until you see the Domestic
Hot Water screen (Fig. 114).
Fig. 114 – Domestic Hot Water
An entry on this screen allows you to give
priority to the DHW function.
Setup Type 2 –
As a second option, a system can be set up so that
only one or two boilers respond to a demand for
domestic hot water. This allows the other boilers in
the system to continue to service the demand for
central heating. This system is more flexible, but the
setup is a bit more complicated:
• All of the boilers are tied together in the
normal way, using the Modbus connections.
• The DHW demand must switch over a whole
boiler (including both burners), not just a
single burner. Both burners in a boiler should
always use the same setpoint.
• The plumbing must be set up so that, during
DHW demand, each boiler used for DHW
is pumped by the DHW pump, and the
boiler pump is turned off. This will keep the
temperature zones separate.
• Each of the boilers that will handle DHW is
wired with an input from the aquastat used to
indicate DHW demand. The aquastat demand
should be jumpered from the Primary control
in each boiler (terminals 5 and 6 on TB6 to
terminals 7 and 8 on TB6).
• The LL CH setpoint used by all of the boilers is
set in the normal way, working from the Lead/
Lag section of the software.
• On each of the boilers used for DHW, priority
is given to the DHW function. Because this
affects individual boilers, rather than the whole
system, this part of the setup is done from
outside the Lead/Lag system.
• On each of the boilers used for DHW, the two
burners in that boiler will operate in Lead/Lag
mode. You can think of each of these boilers
as a separate two-burner Lead/Lag system.
Once a system is set up this way, if there is no DHW
demand, the system will operate like any other
Lead/Lag system. If a demand for DHW arrives,
the boilers used for DHW will stop providing heat
for central heat. On the DHW boilers, the pump(s)
for the DHW loops will start, and those boilers will
provide heat to just the indirect water heaters.
Because this affects an individual boiler, and not the
whole Lead/Lag system, the configuration is done
from outside the Lead/Lag section of the software.
Remember that the boiler includes two controller/
burner combinations. You have to set the DHW
priority on both of the controller/burners.
1.
Start at the 'home' screen. Press the icon for
the controller you want to configure.
2.
The Status Summary page for that controller
will appear. Press the Configure button.
3.
The system will present the Configuration
Menu screen. Scroll down until you see the
line labeled "DHW Priority vs CH."
Fig. 115 – DHW Configuration Screen
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Troubleshooting
