Out of production – LAARS HP-M2 Series - Installation, Operation and Maintenance Instructions User Manual
Page 22
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LAARS Heating Systems
6.
Clean the finned tubing with a wire brush and
vacuum all loose material from the combustion
chamber.
7.
Replace all parts in the reverse order in which
they were removed.
8.
Restart the unit as indicated by the lighting
instruction label.
11C. Unit Pump
The unit pump operates whenever there is a call
for heat or hot water.
It is a wetted-rotor type pump and should always
be filled with water when it is operating so that it will
cool properly.
If a pump change is required for any reason,
valve off the boiler and drain approximately 1 or 2
gallons of water from the unit. Turn off the main
disconnect switch and unplug the pump wires, remove
the pump motor. The pump housing need not be
removed. The replacement pump motor should be
installed in the reverse order from which the old pump
motor was removed. After filling the system be sure to
bleed the coil.
NOTE: If the pump motor is not defective the
pump cartridge alone may be changed (Taco Pumps
Only).
11D. Gas Valve
The gas valve is a solenoid operated, negative
pressure regulated valve. The outlet pressure is
regulated at minus 0.2 inches w.c. It is designed to
operate with supply pressures of 4-13 inches w.c.
Within that range of supply pressures, the regulated
discharge pressure may vary from minus .05 to minus
.35 inches w.c. The regulator is not adjustable and the
effect of this variation in discharge pressure is not
significant. Because of the fixed regulator setting, gas
flow must be adjusted by changing the gas orifice.
To remove the gas valve, shut off 120 volt power
and the master gas cock in gas line, loosen the nut on
the gas orifice union and remove the orifice union plus
piping to the gas valve. Disconnect the wires from the
gas valve. The valve may now be unscrewed from the
inlet piping. It may be necessary to deflect the inlet
piping somewhat in order to clear the boiler jacket.
After the valve has been removed, replace with a new
valve in the reverse order in which the old valve was
removed. Do not over tighten the fittings into the
valve body as this may cause damage to the valve.
NOTE: When fueled by LP gas, H Series
perform best with 9-10 in. W.C. supply pressure. If no
other appliances are being supplied by the LP supply
set the low pressure regulator to 9-10 in. W.C.
11E. Safety Limit Switch
The Safety Limit Switch has a fixed set point at
215°F. It will reset automatically.
To replace the switch , shut off the 120 volt
power and valve off the boiler, drain 1 or 2 gallons of
water from the boiler and remove the nut which holds
the safety limit bulb in the boiler discharge fitting.
Remove the bulb from the fitting and remove the 2
screws which hold the switch assembly to the
electrical control box. Disconnect the 2 wires from the
quick connects at switch and remove the safety limit
assembly. To replace, perform the same operations in
reverse. Push the sensing bulb as far into the fitting as
possible before tightening sealing nut. No more than
1/2" of sensing bulb should be visible after
installation. Fill the boiler and be sure to bleed the coil
at the coil bleed petcock. Turn on disconnect switch
and check boiler operation.
11F. Operating Control
The Operating Control maintains boiler
discharge temperature between 170-210°F during the
space heating cycle. It has a fixed set point of 210°F
(HW-M2 Series only) and a differential of 40°F,
therefore, its contacts open at 210°F and they reclose
at 170°F. If replacement is necessary, shut off the 120
volt power and disconnect the wires to the sensor.
Valve off and drain 1 or 2 gallons of water from the
boiler and remove sensor. Install new sensor, refill
boiler and bleed coil at coil bleed petcock. Check
boiler operation after installation of new Operating
Control. The Operating Control on the H(P)-M2 series
has a fixed set point of 185°F. Its contacts open at
185°F and they reclose at 160°F.
11G. Igniter
The igniter is a “glow bar” type silicon carbide
unit. It is energized whenever there is a call for heat
and the red "IGNITER" light on the boiler control is
lit. After the igniter is switched off and the boiler
continues to run, the igniter functions as a flame
sensor for the boiler control.
If the ignitor fails and must be replaced, always
install a new igniter gasket with the replacement
igniter.
Caution
Ignitor gets hot.
11H. Pressure Differential Switch
The Pressure Differential Switch is a normally
open single pole switch which is designed to detect
pump operation and water flow. To replace, turn off
electrical power & boiler feed water. Valve off and
drain 1 or 2 gallons of water from the boiler, unplug
wires from the switch and remove switch. Install new
switch in reverse order. Refill boiler and bleed air
from the coil bleed petcock. Turn on electrical power
and recycle system.
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