LAARS HP-M2 Series - Installation, Operation and Maintenance Instructions - Manual (Page 24)

Page 24 LAARS Heating Systems
and actuator are on the system side. Close union, open
valves, refill and bleed system, bleed coil at coil bleed
petcock and restart boiler.
11Q. Time Delay Relay (TDR)
(H(P)-M2-series only)
The Time Delay Relay controls the unit pump
and keeps it operating for approximately one minute
after the blower post purge stops. Control voltage on
the TDR is 24 volts from the limit circuit. The
contacts to supply pump power are 120 VAC. They
delay on open one minute after the 24 volt control
voltage is interrupted. Turn off disconnect switch
before changing TDR.
11R. DHW Coil Replacement
Shut off boiler feed water, domestic water supply
to coil and electrical power to boiler. Valve off system
and drain the water from the tank. Disconnect boiler
discharge union from coil fitting, remove relief valve
discharge piping and cut the horizontal hot and cold
water pipes about 6 inches away from plate.
Disconnect and remove low limit sensor. Remove the
six coil retaining nuts and take out coil. Remove the
old coil gasket and clean gasket sealing surface on
tank. Remove the pressure relief valve from old coil
and install in new coil assembly with thread sealing
tape or pipe joint compound. Install new gasket in
recess on tank (if it doesn’t fit snugly in tank recess
remove it and stretch it). Place new coil in tank and
screw on coil retaining nuts. Tighten nuts evenly to
seat gasket properly. Do not over tighten. Make up
boiler discharge union, fill boiler and check around
gasket for leaks. If the coil plate is leak tight make up
hot and cold water pipes with slip couplings and
reassemble relief valve discharge piping. Connect and
reinstall low limit sensor. Turn on domestic water
supply and electrical power. Bleed air from coil bleed
petcock and recycle boiler. Boiler fill pressure is 12
PSI minimum.
11S. Tank Replacement
The tank can be replaced by disconnecting the
DHW coil as explained above and unbolting the lower
pump flange bolts. Access to the tank is possible by
removing the jacket lower front panel. This is done by
removing the screws that hold the panel at the base
and by cutting an aluminum pop rivet on each side at
the top approximately 2 inches down. These rivets
hold the lower front panel to the jacket back. A flat
bladed tool like a putty knife is ideal for this purpose.
Drive the blade down from the top in the crease
between the jacket back and the lower front panel.
This will cut the rivets. Remove the four screws that
hold the electrical box and move it aside. The lower
front panel may now be lifted up above the base and
removed. When the boiler is shipped from the factory
there are shipping bolts which hold the tank and the
base together. The installer was instructed to remove
these bolts before installing the boiler. If this was done
nothing will be holding the tank in place at this time
except the hydronic piping at the rear of the appliance.
Remove the supply and return connections and
remove the tank. Installation of the new tank is done
in the reverse order. If the tank alone is being replaced
it is easier to remove tank and coil together and
change the coil from the old tank to the new one when
both are free of the jacket.
SECTION 12.
Symptom Evaluations
12A. Delayed Ignition
Possible Causes - Time of occurrence
a. High lockups on LP - occurs on start-up.
b. Gas valve regulation problem - occurs on start-up.
c. Defective burner (flameholder) - occurs
primarily on burner shutdown
d. Natural gas orifice in LP unit - occurs on start-up
High lock up pressures on LP fuel systems are
the most common cause of delayed ignitions on H
Series boilers. The high LP supply pressure results
from improper second stage regulator selection or a
faulty regulator.
It can be detected by measuring the gas supply
pressure to the unit at the inlet pressure tap on the gas
valve. Use a water manometer or pressure gage with a
scale reading of at least 25 in. W.C. or 15 oz/in².
Install the pressure tap in the 1/8' NPTF plugged port
located above the gas inlet port on the gas valve. The
gas supply to the boiler must be shut off before
making this connection. The H Series boiler is
designed to operate with supply pressures of 4-13 in.
W.C. (2.3 - 7.5 oz/in²). If supply pressure exceeds 13
in. W.C. (7.5 oz/in²) with the boiler not operating it is
likely that this is the cause of the delayed ignition.
Lock up pressures must be measured when the boiler
is not operating and preferably immediately after
boiler shutdown.
Gas valve regulation problems can also cause
delayed ignitions. To detect gas valve regulation
problems it is necessary to have an inclined
manometer or a Magnehelic pressure gage. The
normal gas valve regulator setting is - 0.2 in. W.C. It
is measured between the 1/8" NPTF plugged port
marked PRESS TAP on the gas valve and the barbed
fitting above the air orifice coupling.
The pressure will be about -2.5 IN. W.C. when
the blower is running (prepurge) before the gas valve
opens. When the gas valve is energized and the
solenoid opens the pressure should rise to - 0.2 IN.
W.C. This should happen smoothly without allowing
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