HS-TARM EXCEL CONTROLS OPERATION SEQUENCE Rev. 4/25/03
1 MECHANICAL SETUP The Tarm EXCEL boiler is a wood-fired boiler with oil or gas backup
burner.
System may be installed with an optional heat storage tank (HST)
1.1 120 volt backup burner (oil or gas) with TT terminals for control.
1.2 120 volt forced draft fan provides combustion air.
1.3 When circulator “C-3” turns on, it circulates water through the boiler while it is warming. As
THERMOVAR tempering valve opens, it circulates water to the heat storage tank (or to heating
loops if circulator C-1 or other heating loop circulator(s) is running). For systems with no HST,
circulator “C-3” runs only if a heating loop is calling for heat.
1.4 Circulator “C-1” circulates water through the heating loops.
2 CONTROLS EXTERNAL TO THE PANEL
2.1 Emergency cut-off switch de-energizes panel.
2.2 Fire-o-matic thermal sensor de-energizes panel.
2.3 Smoke temperature sensor senses stack temperature.
2.4 In optional HST, Honeywell L8151A aquastat senses tank temperature, LO set at 150°F
starts
backup burner when no wood fire is burning. HI set at 160°F
stops backup burner.
2.5 Honeywell L8124C aquastat controls system functions. LO set at 210°F controls overheat
functions, HI set at 180°F is the operating temperature for all modes.
2.6 Honeywell L6081A aquastat controls system functions. LO set at 165°F.
For HST systems this
starts circulator “C-3” when boiler temperature is up to this setting. HI set at 200°F provides high
back up temperature limit for all modes.
2.7 In all aquastats, DIFF (set at 10°F) is the operating differential for LO. The operating differential for
HI is fixed at 10°F.
3 CONTROLS IN THE PANEL
3.1 Top switch provides on/off control and resets the automatic backup mode.
3.2 Bottom switch is the mode selector switch.
3.2.1 Auto backup.
3.2.2 Wood only.
3.2.3 Backup only.
3.3 Five minute timer for draft fan override.
3.4 Relay CR1 provides overheat control.
3.5 Relay CR2 provides lock-off draft fan when fire goes out.
3.6 Adjustable time delay allows time for stack to warm up at start up. (Section 4 below assumes the
typical setting of approx. 15 minutes).
3.7 Relay CR3 control the backup burner.
3.8 Transformer provides 24 VAC power.
4 OPERATION SEQUENCE AND TECHNICAL INFORMATION
Refer to wiring schematic and field wiring diagram for specific plumbing plan. System may be
operated one of three modes as selected by the mode selector.
4.1 Auto backup mode. This description assumes a cold startup with a wood fire starting to burn.
4.1.3 Draft fan operates as follows. Power passes through the on/off switch, the L8124C LO (which
opens during overheat), the L8124C HI (which opens when operating temperature is achieved),
the L6081A HI (which is set higher than the L8124C HI and opens as backup high limit), and a
N.C. (normally closed) contact 8-2 on CR2 (which opens for auto backup function, “fire out,” or if
system is set to backup burner) to terminal F for the 120V draft fan.
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