Page 227

NORA Oilheat Technicians Manual

Chapter 11 Primary Controls Chapter 11—Primary Controls 11-3 Introduction The safe, automatic operation of an oilheat system is dependent on the interaction between: • The thermostat, which opens and closes a circuit based on temperature changes in the heated space. • The limit control, which opens and closes a circuit based on temperature or pressure changes in the boiler or furnace. • The primary control, which regulates the operation of the oilburner. In a properly designed, installed, and serviced oilheat system, these three components work together to safely satisfy a call for space heating, cooling, or water heating. In a typical oilheat system, line voltage flows in a series circuit from the fuse or circuit breaker to a remote toggle (on/off) switch located away from the heating unit. From there, it continues to a service switch at the oil-fired appliance, then to the limit controls, and then to the primary control, which distributes power to the oilburner components (motor, igniter and oil valve). Functions of the primary control The primary control has three main functions: 1. To respond to the thermostat 2. To respond to the limit control 3. To control the startup, run cycle, and shutdown of the oilburner. All primary controls, whether old thermo-mechanical or modern microprocessor, operate on the same basic principles. The primary control accomplishes its mission by: • Reacting to the presence or absence of flame • Managing oilburner startup by checking for a flame before energizing ignition transformers (or igniters), burner motors, and oil valves. • Supervising burner shutdown once the thermostat is satisfied or the limit control opens. All primary controls have line voltage (120 VAC) circuits. In a basic heating system, line voltage is supplied to the primary control through the high limit control when the temperature, in a water heater, boiler or furnace, or the pressure, in a steam boiler, is below the limit setting. Once the limit control is satisfied, it breaks, or opens the circuit, de-energizing the primary control and shutting down the burner. Most primary controls also have low voltage circuits (24 VAC) to accommodate thermostats and/or other devices. The low voltage circuit is closed when the thermostat senses the need for an increase in room Chapter 11 Primary Controls


NORA Oilheat Technicians Manual
To see the actual publication please follow the link above