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NORA Oilheat Technicians Manual

11-4 Primary Controls additional control. For example, a steam boiler with a domestic hot water coil will normally have an aquastat wired to the low voltage terminals on the primary control. This enables the boiler to maintain domestic hot water even when the room thermostat is not calling for heat. Did you know? Power outages do not affect flame detection. If power is lost during a running cycle, the control will NOT go off on safety and it will normally re-energize the burner after power is restored. Flame detection Primary controls detect both the presence and absence of flame. A safety feature of primary controls is that they will not activate the oilburner for startup if the control senses a flame during the off cycle. This prevents additional fuel being pumped into a unit that has a fire before startup. Primary controls must react quickly to the presence or absence of flame while the oilburner is running. The primary control must shut the burner off promptly if no flame is established on startup or if the flame is lost during the run cycle. If the primary control did not shut off the oilburner in these circumstances, the burner Figure 11-1: Parallel wiring for 24v thermostat and aquastat to the primary Figure 11-3: Cad cell and its wiring symbol Chapter 11 Primary Controls Figure 11-2: Honeywell RA117a primary control temperature. When the heat reaches the right temperature and the thermostat is satisfied, it opens the circuit. For the primary control to activate the oilburner, both the line and low voltage circuits must be closed. In most cases, that means that if either the thermostat or the limit control is satisfied (open) the primary control will not activate the oilburner. In systems with a line voltage thermostat, or with a low voltage thermostat connected to controls other than the primary control, a jumper is placed between the primary’s thermostat terminals, permanently closing the low voltage circuit, Figure 11-1. The primary control is activated solely by the limit control. Some systems have an additional control wired in parallel with the thermostat. In those cases, the primary’s low voltage circuit can be completed through either the thermostat or the Thermostat Aquastat Primary Control Bimetal Element Ignition Relay (RA117 only) Mounting Bracket Recycle Adjust Lever Lever to Put Contacts “In Step” Ignition Timing Adj. (RA117 only) Motor Relay Reset Lever on Safety Switch Transformer


NORA Oilheat Technicians Manual
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