Laars NeoTherm NTH Installation and operation instructions manual - page 33
NeoTherm Boiler
Page 33
12.
Place the appliance in operation according to
Section 6.2
checking all gas connections for leaks.
Confirm all fasteners are tight.
7.2.9 Gas Pressure Switches
(optional)
The high and low gas pressure switches are 24V
manual reset switches that act to cut power to the gas
valves if the gas pressure is too low or too high for
proper operation. The gas pressure switches used are
integrally vent limited, and do not require venting to
atmosphere. To remove a switch, remove the screw on
the plastic housing and pull the clear cover off.
Disconnect the two wires from the screw terminals.
Twist the switch off the pipe nipple. Reassemble in
reverse order. For natural gas, set the low gas pressure
switch to 3" w.c. For propane, set the low gas pressure
switch to 5" w.c. For natural and propane, set the high
gas pressure switch to 14".
SECTION 8.
Trouble Shooting
8.1 Sequence of Operation
The NeoTherm appliance is a cold start appliance
that should start only on a call for heat from a tank
aquastat, room thermostat, zone valve end switch or
other space temperature control device.
1.
Upon a call for heat: (a) the internal pump and
system pump will start; (b) the blower will begin a
30 second pre-purge.
2.
Following the prepurge cycle the direct spark
ignition will spark and will begin a 4 second trial
for ignition. The unit is allowed one or three
ignition retries.
3.
The gas valve will then be energized and a reduced
rate ignition will occur. The unit will remain in a
reduced rate start-up period for several seconds.
4.
After the reduced rate start time is over, the unit
will be in normal operation. Firing rate will
modulate based on the heating load via the
temperature controller settings and readings.
5.
When the call for heat is complete, or the unit reaches
its setpoint temperature, the gas valve will close, and
the fan will continue to run for its 20 second post-
purge. If a pump delay time is used, the pump will
continue to run for the specified amount of time
(adjustable from 0.1 to 10 minutes).
8.2 Short Cycling
Because the NeoTherm is a modulating boiler, and
its input will decrease when there is a reduction in
heating load, short cycling is greatly reduced. If the
heating load drops below the minimum input of the
boiler for an extended period, the boiler will have a
tendency to short cycle. This can be a symptom of
improper control strategy or setpoints, or a load
distribution problem. The NeoTherm control has a built-
in anti-short cycle (ASC) feature. The ASC is a timed
setting that will delay the boiler start for a specified
time after one call for heat is completed. The ASC time
may be adjusted as desired (see
Sections 5.2.2
and
5.2.2.6
for more information).
8.3 Error Codes -
See
Table 14
.