LAARS NeoTherm LC NTV1700 - Install and Operating Manual - Manual (Page 98)

LAARS Heating Systems Page 94
Section 12
TROUBLESHOOTING
12.1 Potential Setup and
Synchronization Problems
Because the NeoTherm LC uses a sophisticated
control system, it can constantly perform a series
of self-checks. For example, as a burner is lighted,
the controller checks each stage of the purge and
ignition process. If part of the process does not
happen on time, or takes too long to occur, the
controller stops the process. We have detailed these
self-checks in the section on “Operating Sequence.”
Two of these self-checks are particularly important:
• Controller synchronization
• Flap valve status
If the control system is not satisfied with the results
of both of these checks, it will not allow the system
to run. Sometimes the reason for this may not be
obvious at first – that’s why we are describing them
at the start of this section on Troubleshooting.
Operator
interface
Boiler 1
Slave 4
Boiler 2
Slave 3
Slave 2
Lead Lag
Master and
Slave 1
Slave 6
Boiler 3
Slave 5
Slave 8
Boiler 4
Slave 7
Addr
1
Addr
2
Addr
3
Addr
4
Addr
5
Addr
6
Addr
7
Addr
8
Fig. 122 – Lead/Lag Arrangement in a Multiple-Boiler Installation
12.1.1 Controller Synchronization
On a multiple-boiler installation, the individual
boiler controllers are arranged in a “daisy chain”
using a Modbus connection, with the Secondary
control of one boiler connected to the Primary
control of the next boiler. Up to four boilers, with
up to eight controllers, can be connected in this way.
See Fig. 122.
As part of the setup process, each of these
controllers must be given a unique address. (For
details, see Section 9 - Installation and Setup.” The
controls must be set up and addressed correctly
before the Modbus wiring is completed. If the wiring
is attached before the Modbus control addresses are
changed, there will be multiple controls with the
same address, and the system will not work.
When a Lead/Lag system is first powered up, the
controller acting as the Lead/Lag Master goes
through a “synchronization” process. During
synchronization, the controller establishes
communications with each of the Slave controllers
via the Modbus link. The Slave controllers
download some setup parameters and operating
history information. (On a system with several
boilers, this phase can take several minutes.) If the
Master cannot establish communications with one of
the Slaves, it triggers a Hold or Lockout.