LAARS EDN Series - Installation, Operation and Maintenance Instructions - Manual (Page 22)

Page 22 LAARS HEATING SYSTEMS
This is done by removing the screws that hold the
panel at the top and lifting the panel away. Isolate the
appliance and drain down using the drain cock at the
base of the tank. Remove the tank sensor. Undo the
union and the pump flange bolts that connect the tank
to the boiler, unscrew the panel between the upper and
lower compartments, support the upper components
and remove the tank. Installation of the new tank is
done in the reverse order. After installation purge all
air from the boiler before restarting.
7.9 Thermostatic Union (EDP/EDN)
The thermostatic union is a 1¼" NPTF union
which must be mounted at the flow outlet to control
boiler temperature. The union must be installed so that
union nut is on the boiler side of the connection. This
insures that the thermostat is properly positioned with
its spring facing up, toward the system. The element
has two small bypass holes that allow some water to
flow into the system at all times. When the boiler first
starts and the element is closed, boiler water is re-
circulated back to the return until the supply water
reaches 160°F (71°C). The element then modulates
open. If the temperature does not exceed 150°F (66°C)
within two minutes after firing, the element is not
functioning properly. To replace the element, shut off
and drain the section of the system adjacent to the
thermostatic union. Open the union and replace the
element with a new one. The element should be
installed so that its spring and actuator are facing the
system side (up). Close the union, open the valves,
refill and bleed the system. Ensure that air is venting
from the air vent on top of the boiler chamber and it is
left operational. Restart boiler.
7.10Cleaning the Boiler Coil
The Endurance is equipped with a premixed
combustion system. This type of combustion system
does not create free carbon (soot) except in very rare
instances and therefor the combustion chamber coil
will probably never need cleaning. If cleaning is
required, proceed as follows: valve off the boiler,
switch off the electrical power at the disconnect
switch, drain 1-2 gallons (4-8L) of water from the
boiler drain, remove the flue assembly from the top of
the boiler, remove the pump flange bolts from the top
pump flange, disconnect the sensor wires from the
sensors (boiler flow, return and safety limit), undo the
union nut from the boiler flow manifold, and remove
the four (4) screws from the bottom gas valve flange.
The boiler assembly may now be removed from the
jacket. After removal of the boiler assembly from the
jacket, remove the four (4) long screws that secure the
top and bottom pans. Remove the air vent and the top
pan. Remove the insulation retainer and the coil cover
insulation. Clean the boiler coil with a wire brush and
vacuum debris from the combustion chamber (avoid
hitting the ignitor or the flame sensor with the brush or
vacuum hose because they are fragile).
After cleaning, assemble the parts in the reverse
order, open isolation valves and bleed air from the
boiler and the system. Follow the lighting instructions
and start the boiler. Check operation.
SECTION 8
Servicing.
8.1 Sequence of Operation
Figures 22 and 23 depict the flow paths and
temperature sensor locations for the space heating,
EDP/EDN, and the combined space heating and
domestic water heating, EBP, appliances.
The model EDP/EDN modulating boilers are
cold start boilers that will start only on a call for heat
from a room thermostat or zone control contact.
During normal operation the Message Center [MC]
LED display will indicate ‘ON’ while awaiting a call
for heat. On a call for heat the following sequence
will occur.
1. (a) The internal pump will start.
(b) After 5 seconds the blower prepurge cycle
will start and operate for approximately 6
seconds while the [MC] indicates alternately
and the current boiler outlet temperature.
2. Following the prepurge cycle the ignitor will
heat for 10 seconds while the blower continues
to operate.
3. The gas valve will then be energized (green ‘GV’
LED located on the PCB next to the display will
light) and open, gas will flow and ignition will
occur.
4. 10 seconds after establishing combustion and
proof of flame ( via the flame rod signal to
ground ), the ignitor will be de-energized and
the burner will modulate to high fire for
maximum output.
5. The [MC] should indicate a rapid rise in
temperature to 150º F (1-2 min. duration).
During this period the thermostatic union at the
flow outlet is closed and the boiler is operating in
the internal recirculation mode. [Service note: If
the temperature rise is not rapid the union
thermostat may be defective and must be
replaced].
6. At 150° F the thermostat will allow increased
flow to the system and a gradual rise in
temperature will be indicated until the
temperature approaches the setpoint temperature
of 180ºF. The firing rate will start to modulate
downward until its cutoff limit is reached or the
call for heat is satisfied.