LAARS NeoTherm NTV (Sizes 150–850 MBTU/h) - Install and Operating Manual - Manual (Page 62)

Page 58 LAARS Heating Systems
Section 11 -
OPERATING DETAILS AND
TROUBLESHOOTING
11.1 Normal Startup and Initialization
When power to the unit is turned on, the controller will
automatically go through a startup and initialization
procedure. At first the interface will display some
information about the control software. See Fig. 48.
Fig. 48 – First Initialization Display
Next, the interface will search for the SOLA controller that
will actually control the boiler. See Fig. 49.
Fig. 49 – Second Initialization Display
Once the interface makes the connection to the controller,
it will display the address it is using to communicate (the
“Modbus address”). The interface will download a series of
values from the SOLA controller (or “synchronize” with the
controller).
When the synchronization is finished, the display will change
to the Home screen shown in Fig. 27.
11.2 Sequence of Operation
The NeoTherm is a cold-start appliance. It should start only
when it receives a call for heat from a tank aquastat, room
thermostat, zone valve end switch or other space temperature
control device.
1.
The unit receives a call for heat.
2. The controller checks the safety chain.
3. The fan starts and waits to achieve prepurge RPM.
4. The prepurge timer is started once the prepurge RPM is
achieved.
5. There is a pre-ignition time of two seconds to check the
flame sensor operation and status. During this period an
intermittent spark can be seen.
6. Next there is a trial for ignition period of four seconds.
The direct spark ignition switches to constant spark
for three seconds. During this time the gas valve is
open. For the last second of the ignition period, direct
spark is de-energized and the flame sensor checks for
established flame. If flame is sensed, the control enters
Run to satisfy the demand. If flame is not established,
the control enters a retry, starting from step 2. If flame
has not been established after the preset number of
retries, the control will lockout with a 109 error code.
7. The call for heat signal is removed.
8. The gas valve shuts off.
9. The fan and pump continue to run for the over-run
times to purge the system.
This is the basic operating sequence of the appliance for a
DHW or hydronic call for heat.
11.3 Modulation Control
The control uses a PID algorithm to adjust the firing rate of
the boiler as the control point is approached. The goal of
the control is to operate at a minimum firing rate to match
the load on the appliance. This is done by using a setpoint,
and on/ off differentials. The control modulates to achieve
the setpoint temperature, which could be several degrees
away from the actual off point. The off point is calculated by
adding the setpoint plus the off differential. The setpoint and
differentials used in operation are dependent upon the type of
call for heat being applied. If there is a DHW call, the DHW
setpoint and off differentials are used. If there is a hydronic
call, the CH setpoint and off differentials are used. When
the setpoint plus the off differential is reached, the control
prevents the unit from firing until the water temperature
reaches the setpoint minus the on differential.
11.4 Pump Control
The control can operate three pumps. The boiler pump is
active any time there is a call for heat applied to the control.
The DHW and system pumps are active based upon the call
and priority of the heat demand being supplied. When there is
a hydronic call supplied, the system pump is active. If there
is a DHW call supplied while the hydronic call is active,
with DHW priority enabled, the system pump turns off and
the DHW pump turns on. Domestic hot water priority forces
the control to attempt to satisfy the domestic water demand
before the hydronic demand. Once the last heat demand has
been satisfied, the boiler pump enters an overrun time.