OFTEC Oil Burner Types and Operation 4 — Questions and Answers
Question 1: What does the term 'delayed ignition' mean in relation to oil burners?
- Oil is being delivered but fails to ignite immediately, causing a build-up (Correct answer)
- The thermostat takes too long to respond
- The boiler water heats slowly
- The flue damper opens late
Correct answer: Oil is being delivered but fails to ignite immediately, causing a build-up
Delayed ignition occurs when atomised oil enters the combustion chamber but does not ignite immediately. When it does ignite, the accumulated oil vapour causes a potentially dangerous 'puff back' or small explosion.
Question 2: What is the correct electrode gap setting typically specified for a domestic oil burner?
- 3-4mm between electrode tips (Correct answer)
- 10-12mm between electrode tips
- Less than 1mm between electrode tips
- 15-20mm between electrode tips
Correct answer: 3-4mm between electrode tips
The standard electrode gap for most domestic oil burners is approximately 3-4mm. Too narrow a gap may cause carbon bridging, while too wide a gap may prevent spark generation. Always refer to the manufacturer's specifications.
Question 3: Why must an oil burner fan run for a pre-purge period before ignition?
- To clear any residual oil vapour from the combustion chamber (Correct answer)
- To warm up the motor
- To build up oil pressure in the pump
- To heat the electrodes
Correct answer: To clear any residual oil vapour from the combustion chamber
The pre-purge period allows the fan to push fresh air through the combustion chamber, clearing any residual oil vapour that could cause a dangerous puff back when ignition occurs. This is a critical safety feature.
Question 4: What is the purpose of the fire valve in an oil supply system?
- To automatically shut off the oil supply in the event of a fire (Correct answer)
- To regulate the flow rate to the burner
- To filter contaminants from the oil
- To allow the tank to be drained for cleaning
Correct answer: To automatically shut off the oil supply in the event of a fire
A fire valve is a fusible link valve installed on the oil supply line near the appliance. In a fire, the fusible link melts (typically at 68°C), closing the valve and cutting off the fuel supply to prevent the fire being fed.
Question 5: What is a common cause of oil burner short cycling?
- An oversized burner or incorrect thermostat differential (Correct answer)
- A blocked flue
- An empty oil tank
- A faulty fire valve
Correct answer: An oversized burner or incorrect thermostat differential
Short cycling occurs when the burner fires and shuts down too frequently. Common causes include an oversized burner for the heat load, too narrow a thermostat differential, or a faulty aquastat. This reduces efficiency and increases wear.
Question 6: What does a solenoid valve do in an oil burner system?
- Electrically opens and closes to control the flow of oil to the nozzle (Correct answer)
- Creates the ignition spark
- Detects the flame
- Regulates the fan speed
Correct answer: Electrically opens and closes to control the flow of oil to the nozzle
The solenoid valve is an electrically operated shut-off valve in the oil supply. It opens when the burner control box calls for heat and closes immediately when the burner stops, preventing oil from dripping into the combustion chamber.
OFTEC Oil Burner Types and Operation 4
What does the term 'delayed ignition' mean in relation to oil burners?