4.1.2 Warmup cycle. Power passes from the L8124C (as above) through a N.C. contact 11-3 on
CR3(which opens when backup burner is running), through the smoke temperature
sensor(which
opens when stack achieves temperature setting), to the time delay module. If stack
temperature is achieved in less than 15 minutes, smoke sensor opens, this timer will stop timing
and draft fan will continue operating. If at any time after L8124C HI (operating temperature) is
closed, the smoke temperature sensor stays closed due to the stack not warming for more than
15 minutes, this delay will activate and turn on relay CR2 which locks on.
4.1.3 Automatic backup function. Draft fan operates controlled by the L8124C HI (operating
temperature) until fire is out and stack temperature is below sensor setting for 15 minutes. Then
draft fan stops and backup burner operates. Once relay CR2 is activated, CR2 N.O. (normally
open) contact 7-4 closes to lock relay CR2 on which may be reset by turning off the on/off/reset
switch. CR2 N.C. contact 8-2 opens, stopping the draft fan. CR2 N.O. contact 9-6 closes. For
systems with no HST, relay CR3 turns on immediately. For HST systems, if the L8151A LO is
closed(HI will be closed),relay CR3 energizes. CR3 N.O. contact 10-6 closes to lock on CR3
until HI temperature has been achieved. The L8151A continues to maintain storage tank
temperature between HI and LO settings. CR3 N.O. contact 9-5 closes to activate the backup
burner by shorting TT. Although this contact controls the burner, the actual power for the burner
passes through the two aquastats just as it does for the draft fan. For HST systems, CR3 N.O.
contact 8-12 closes to allow circulator “C-3” to run while burner is running. CR2 N.C. contact 1-
7 opened this circuit. After system, is in back-up mode, the C-3 circulator should only run while
the burner is running to prevent circulation of warm water from the heat storage tank to the
boiler. CR3 N.C. 11-3 opens while backup burner is running to prevent a “hot” back feed
through the smoke temperature sensor to the orange wire which is controlled by the L8124C.
4.2 Wood only mode. This mode operates similarly to the auto backup mode. The basic difference
is that when the draft fan stops, the backup burner does not start. There are no changes for the
items discussed in 4.1.1 and 4.1.2 above. Once relay CR2 is activated, CR2 N.O. contact 7-4
closes to lock relay CR2 on which may be reset by turning off the on/off/reset switch. CR2 N.C.
contact 8-2 opens, stopping the draft fan. For HST systems. CR2 N.C. contact 7-1 opens to
stop circulator “C-3.” This prevents the circulation of warm water from the heat storage tank to
the boiler. Although CR2 N.O. contact 9-6 closes, the mode selector switch prevents CR3 from
energizing.
4.3 Backup mode only. In this mode, the backup burner operates and the draft fan does not. The
mode selector switch directly energizes relay CR2. The details of operation are basically the
same as what is given under automatic backup function (4.1.3) above. The smoke sensor does
not provide any control function in this mode.
4.4 Overheat function. Since an active wood fire cannot easily be “stopped” boiler overheating can
occur. If boiler temperature rises in spite of the draft fan not running (L8124C HI and L6081A HI
are open), L8124C LO (set at 210°F) close on rise contact R-W will close, energizing relay CR1.
For HST systems, CR1 N.O. contact 5-3 closes to start circulator “C-3” if for any reason it is not
running. CR1 N.O. contact 6-5 closes to override heat dump zone room thermostat and thereby
take excess heat from the boiler.
4.5 Draft fan timer. Because of the potential for explosion, the doors accessing the firebox should
never be opened while the draft fan is not running. The operator may turn on the draft fan
override timer. This causes the draft fan to operate even though the L8124C HI is open.
4.6 Circulator “C-1” control. In the L8124C, the relay 1-K is available for control of circulator “C-1” or
a heating zone circulator, Whenever the L8124C terminals TT are shorted (as shown on field
wiring diagram), relay 1-K energizes. N.O. contact 1-K2 closes to energize the circulator. The
fact that the N.O. contact 1-K1 closes and overrides the LO open on rise contact does not
present a problem because of the open on rise HI in each of the two aquastats.
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