11 - operating details and troubleshooting, 1 normal startup and initialization, 2 sequence of operation – LAARS NeoTherm NTV (Sizes 150–850 MBTU/h) - Install and Operating Manual User Manual

Page 62: 3 modulation control, 4 pump control

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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.

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