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HVAC Excellence Oil Heat study materials
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HVAC Excellence Oil Heat Certification practice questions

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Question 1Oil Heat (Oil-Fired Heating Systems)

A technician is setting up an oil furnace and needs to establish the correct draft overfire for a conventional natural-draft unit. Which draft condition is normally targeted at the breach?

  1. An alternating draft that swings from negative to positive each cycle
  2. A neutral pressure of exactly 0.00 in. w.c.
  3. A steady negative pressure of roughly -0.02 to -0.04 in. w.c. Correct answer.
  4. A positive pressure of about +0.10 in. w.c.

Explanation

Conventional oil furnaces are designed to operate with a slight negative pressure at the breach, typically around -0.02 to -0.04 in. w.c., which keeps combustion products moving up the flue without excessive heat loss. Positive or neutral breach pressure can allow flue gases to escape into the living space.

Question 2Oil Heat (Oil-Fired Heating Systems)

During a service call, a technician finds the oil burner nozzle marked 0.85 GPH at 80 degrees spray angle. What does the 0.85 rating represent?

  1. The nozzle's maximum allowable pump pressure
  2. The firing rate in gallons per minute
  3. The gallons of oil burned per hour at 80 psi
  4. The nozzle flow rate at 100 psi pump pressure Correct answer.

Explanation

Nozzle ratings are stated in gallons per hour (GPH) at a reference pump pressure of 100 psi. The actual firing rate changes if the pump pressure differs from 100 psi, so the technician must correct the rating for the measured pressure.

Question 3Oil Heat (Oil-Fired Heating Systems)

A single-stage oil burner pump is being replaced. Which pump pressure is the standard reference used when selecting and rating oil burner nozzles?

  1. 175 psi
  2. 50 psi
  3. 300 psi
  4. 100 psi Correct answer.

Explanation

Oil burner nozzles are rated at a standard reference pressure of 100 psi. If the pump is set to a different pressure, the actual flow must be adjusted using the square-root relationship between pressure and flow.

Question 4Oil Heat (Oil-Fired Heating Systems)

An oil-fired appliance uses a barometric draft regulator in the flue connector. What is the primary function of this device?

  1. To increase the flue gas temperature before it enters the chimney
  2. To filter soot from the flue gases before they leave the appliance
  3. To stabilize the draft at the appliance by admitting room air into the flue Correct answer.
  4. To shut off the burner when the flue temperature rises

Explanation

A barometric draft regulator opens to admit room air and thereby holds a relatively constant negative pressure at the appliance, compensating for changing chimney draft. This protects the combustion process from excessive draft that would otherwise pull heat up the chimney.

Question 5Oil Heat (Oil-Fired Heating Systems)

A technician is checking a cad cell flame detection circuit. Which condition should the cad cell see to confirm the flame is established?

  1. An open circuit of infinite resistance across the cell
  2. A resistance above 100,000 ohms across the cell
  3. A low resistance across the cell, typically a few hundred to a few thousand ohms Correct answer.
  4. A steady AC voltage of 24 volts at the cell terminals

Explanation

A cad cell is a photoresistor whose resistance falls when light from the flame strikes it. The primary control interprets a low resistance, generally in the hundreds to low thousands of ohms, as a proven flame.

Question 6Oil Heat (Oil-Fired Heating Systems)

A technician measures the smoke spot on a filter paper and obtains a number 2. What does this result indicate about combustion?

  1. The draft regulator is stuck open
  2. Combustion is clean and no adjustment is needed
  3. Soot is present and combustion should be adjusted or the appliance cleaned Correct answer.
  4. The oil pump pressure is too low

Explanation

The smoke test uses a numbered spot scale where 0 is clean and higher numbers indicate increasing soot. A number 2 spot means soot is present, so the technician should tune combustion and inspect for fouling.

Question 7Oil Heat (Oil-Fired Heating Systems)

What is the purpose of the electrodes on an oil burner?

  1. To measure the flame's light output
  2. To create a high-voltage arc that ignites the oil spray Correct answer.
  3. To regulate pump pressure
  4. To preheat the oil before it reaches the nozzle

Explanation

The ignition transformer applies high voltage across the electrode tips, producing an arc that ignites the atomized oil spray. Electrode gap and position must be set to the manufacturer's specification for reliable lightoff.

Question 8Oil Heat (Oil-Fired Heating Systems)

A technician is preparing to replace a nozzle on an oil burner. Which action is required before removing the nozzle?

  1. Run the burner until it locks out on safety
  2. Open the bleed port while the burner is running
  3. Shut off the burner and isolate the fuel supply, then relieve line pressure Correct answer.
  4. Increase pump pressure to blow out debris

Explanation

Fuel must be isolated and the burner de-energized before service, and residual line pressure should be relieved to prevent a spray of oil. Safe isolation protects the technician from a pressurized oil release.

Question 9Oil Heat (Oil-Fired Heating Systems)

A technician raises pump pressure from 100 psi to 144 psi on a nozzle stamped 1.00 GPH. What is the approximate new flow rate?

  1. 2.00 GPH
  2. 1.44 GPH
  3. 0.83 GPH
  4. 1.20 GPH Correct answer.

Explanation

Nozzle flow varies with the square root of the pressure ratio. The square root of 144/100 is 1.2, so a 1.00 GPH nozzle at 144 psi delivers about 1.20 GPH.

Question 10Oil Heat (Oil-Fired Heating Systems)

An oil burner runs, produces a visible flame, but the primary control trips on safety after the trial-for-ignition period. Which item should be checked first?

  1. The barometric draft regulator setting
  2. The oil tank gauge reading
  3. The cad cell and its wiring for a dirty lens or open connection Correct answer.
  4. The air filter in the return duct

Explanation

A burner that fires but still trips on safety usually has a flame-detection problem: the cad cell cannot see the flame or its circuit is open. A dirty cell lens, misdirected cell, or broken lead prevents the control from proving flame.

Question 11Oil Heat (Oil-Fired Heating Systems)

A technician performs a combustion test and finds a CO2 reading of 9 percent with a smoke number of 1 on a retention-head burner. What is the most reasonable interpretation?

  1. The nozzle is completely plugged
  2. The burner is over-aerated and CO2 is too high
  3. Combustion is reasonable but can likely be improved by fine-tuning air and draft Correct answer.
  4. The pump pressure is far too low

Explanation

A CO2 reading around 9 percent with a light smoke spot suggests the burner is operating but not fully optimized. Adjusting the air shutter and draft to raise CO2 while keeping smoke at zero typically improves efficiency.

Question 12Oil Heat (Oil-Fired Heating Systems)

A two-line oil supply system is being installed with the tank below the burner. Why is a two-line system preferred over a single-line system in this arrangement?

  1. The return line helps purge air and provides a positive supply under lift conditions Correct answer.
  2. It allows the use of a smaller tank
  3. It removes the need for a primary control
  4. It eliminates the need for a nozzle

Explanation

When the tank is below the burner, the pump must lift oil, and a two-line system with a return helps remove air and maintain a steady supply. This improves reliability and reduces air-related lockouts.

Question 13Oil Heat (Oil-Fired Heating Systems)

A technician is checking the operation of a primary safety control on an oil burner. What does the trial-for-ignition period represent?

  1. The time the burner runs after the thermostat is satisfied
  2. The time required to heat the nozzle line
  3. The time allowed for flame to be proven before the control locks out Correct answer.
  4. The interval between oil deliveries

Explanation

The trial-for-ignition period is the interval during which the control permits the burner to run while waiting for a flame signal. If flame is not proven within that time, the control shuts down and locks out.

Question 14Oil Heat (Oil-Fired Heating Systems)

An oil furnace has a dirty heat exchanger and the technician notes reduced airflow and a higher stack temperature. What effect does this fouling have on efficiency?

  1. Efficiency rises because the flue gases are hotter
  2. Efficiency drops because less heat transfers to the air and more leaves up the flue Correct answer.
  3. Efficiency is unaffected as long as the burner fires
  4. Efficiency rises because the blower runs longer

Explanation

Soot and scale on the heat exchanger act as insulation, reducing heat transfer to the supply air. More heat is carried up the flue, so steady-state efficiency falls and fuel consumption rises.

Question 15Oil Heat (Oil-Fired Heating Systems)

A technician is setting electrode spacing on a burner. What is the typical consequence of electrodes set too far apart?

  1. The draft regulator opens wider
  2. The arc may be weak or intermittent, causing delayed or failed ignition Correct answer.
  3. The oil flow rate increases
  4. The cad cell resistance drops

Explanation

Wide electrode spacing raises the voltage needed to strike an arc, so the spark may be weak or erratic. This causes delayed ignition or failure to light, often accompanied by puffback.

Question 16Oil Heat (Oil-Fired Heating Systems)

A technician observes a puffback on startup of an oil furnace. Which condition is the most likely cause?

  1. Excessive combustion air
  2. Delayed ignition from a weak spark or poor electrode position Correct answer.
  3. A clean heat exchanger
  4. A properly set draft regulator

Explanation

Puffback results from accumulated oil igniting suddenly after a delayed lightoff. Weak spark, incorrect electrode gap, or a partially plugged nozzle are common causes.

Question 17Oil Heat (Oil-Fired Heating Systems)

A technician is checking oil tank installation requirements. What is the purpose of the vent pipe on an oil storage tank?

  1. To allow air to enter and exit the tank as oil is consumed or delivered Correct answer.
  2. To drain water from the tank
  3. To measure tank level
  4. To supply oil to the burner

Explanation

The vent pipe equalizes pressure inside the tank as oil is drawn out or delivered, preventing vacuum or pressure buildup. It must be sized and terminated per code, away from openings.

Question 18Oil Heat (Oil-Fired Heating Systems)

A technician is diagnosing a burner that short-cycles. Which condition would most directly cause the burner to cycle on and off rapidly?

  1. A failed cad cell
  2. A dirty blower wheel
  3. A clogged nozzle
  4. A thermostat or aquastat with a narrow differential and rapid response Correct answer.

Explanation

Short cycling often results from a control with too narrow a differential or a sensor responding too quickly, causing the burner to satisfy and restart repeatedly. Checking control settings and sensor placement is the first step.

Question 19Oil Heat (Oil-Fired Heating Systems)

A technician measures a nozzle line pressure of 100 psi but the burner fires poorly with a smoky flame. Which additional factor should be verified before adjusting the nozzle size?

  1. The age of the thermostat
  2. The air shutter setting and draft overfire Correct answer.
  3. The color of the oil tank
  4. The length of the thermostat wire

Explanation

Smoke can result from insufficient combustion air or incorrect draft even when pump pressure is correct. Verifying air shutter position and draft before changing nozzle size prevents misdiagnosis.

Question 20Oil Heat (Oil-Fired Heating Systems)

A burner with a retention head is being converted from a 0.75 GPH to a 1.00 GPH nozzle. What else must be evaluated to maintain proper combustion?

  1. The combustion air settings and the draft overfire Correct answer.
  2. The oil tank vent size only
  3. The thermostat's heat anticipator only
  4. The cad cell resistance only

Explanation

Increasing firing rate raises the air demand and changes draft requirements, so the air shutter, head settings, and draft must be rechecked. Without this adjustment the burner may smoke or run inefficiently.

Question 21Oil Heat (Oil-Fired Heating Systems)

A technician is evaluating an oil-fired boiler with a stack temperature of 650°F and a room temperature of 70°F. Which statement best reflects the significance of this reading?

  1. The reading shows the cad cell is failing
  2. The reading indicates the pump pressure is too low
  3. The reading proves the boiler is operating at peak efficiency
  4. A high net stack temperature indicates heat is being lost up the flue and efficiency may be reduced Correct answer.

Explanation

Net stack temperature is the difference between flue gas and ambient temperature. Excessive net stack temperature signals heat loss up the chimney, often from fouling, excess air, or poor draft control.

Question 22Oil Heat (Oil-Fired Heating Systems)

A technician is diagnosing a burner that locks out intermittently only on cold mornings. Which condition best explains this pattern?

  1. Oil viscosity is higher at low temperature, reducing flow and delaying atomization Correct answer.
  2. The draft regulator is set too low
  3. The nozzle is oversized
  4. The cad cell is too clean

Explanation

Cold oil is more viscous, which can slow flow and impair atomization, especially on a marginal system. This can delay ignition and cause intermittent lockouts on cold starts.

Question 23Oil Heat (Oil-Fired Heating Systems)

A technician is commissioning a new oil-fired appliance and must confirm the draft is stable across the firing cycle. Which method best verifies this?

  1. Measure the thermostat resistance
  2. Measure the oil filter pressure drop only
  3. Measure the tank level before and after the cycle
  4. Measure draft at the breach before, during, and after the burner cycle and compare to the manufacturer's range Correct answer.

Explanation

Draft should be checked throughout the operating cycle because it changes as the chimney warms and the barometric damper responds. Comparing readings to the manufacturer's specified range confirms stable operation.

Question 24Oil Heat (Oil-Fired Heating Systems)

A technician is troubleshooting a burner that fires but produces a heavy smoke spot of 6 with a low CO2 reading. Which combination of causes is most consistent with these readings?

  1. High pump pressure with a clean cad cell
  2. Insufficient combustion air combined with poor atomization Correct answer.
  3. Correct draft with an oversized heat exchanger
  4. Excess combustion air with a clean nozzle

Explanation

A high smoke spot with low CO2 points to a rich mixture: too little air and/or poor atomization. The technician should check the air shutter, nozzle condition, and pump pressure.

Question 25Oil Heat (Oil-Fired Heating Systems)

A technician is evaluating a two-pipe oil system where the return line runs back to the tank. What is the purpose of the bypass plug in the pump?

  1. It routes excess oil to the return line instead of the internal relief port Correct answer.
  2. It locks out the primary control
  3. It filters the oil before the nozzle
  4. It increases the nozzle flow rate

Explanation

In a two-line system the bypass plug directs surplus oil to the return line, allowing continuous circulation and air removal. Without it the pump's internal relief would recirculate oil and the system would not function as intended.

Question 26Oil Heat (Oil-Fired Heating Systems)

A technician is selecting a replacement nozzle for an oil burner. What does the GPH rating stamped on a standard 80-degree nozzle represent?

  1. The volume of oil the nozzle delivers per hour at 100 psi pump pressure Correct answer.
  2. The maximum heat input the burner can produce at 140 psi
  3. The flow rate of oil through the return line at 50 psi
  4. The gallons of oil consumed per full heating season

Explanation

Nozzle ratings are standardized at 100 psi, so the stamped GPH describes flow at that reference pressure. Actual delivered rate changes with the square root of the pressure ratio, which is why pump pressure must be set to the nozzle rating before combustion tuning.

Question 27Oil Heat (Oil-Fired Heating Systems)

Which component on a conventional oil burner transforms the low-voltage thermostat signal into the high-voltage spark at the electrodes?

  1. The stack relay
  2. The nozzle assembly
  3. The cad cell
  4. The ignition transformer Correct answer.

Explanation

The ignition transformer steps up line voltage to the high potential needed to jump the electrode gap and ignite the oil spray. The electrodes only deliver the spark; the transformer is the source of that voltage.

Question 28Oil Heat (Oil-Fired Heating Systems)

A technician is checking a cad cell flame detector. Which condition will cause the cad cell resistance to drop to its lowest value?

  1. The burner has just started and the chamber is dimly lit
  2. The burner is off and the combustion chamber is dark
  3. The burner is running with a bright, steady flame Correct answer.
  4. The cad cell lens is coated with soot

Explanation

A cadmium sulfide cell decreases in resistance as light intensity increases, so a bright stable flame produces the low resistance the control interprets as flame present. Darkness or a dirty lens raises resistance and can cause lockout.

Question 29Oil Heat (Oil-Fired Heating Systems)

Why must the combustion chamber of an oil furnace be allowed to purge before the ignition transformer is energized on startup?

  1. To raise the stack temperature for the draft control
  2. To test the cad cell for light sensitivity
  3. To cool the nozzle body before oil flows
  4. To clear residual oil vapors and prevent a puffback Correct answer.

Explanation

The prepurge removes accumulated fuel vapors from the chamber so ignition does not occur in a fuel-rich condition. Without adequate purge, delayed ignition can produce a puffback or explosion.

Question 30Oil Heat (Oil-Fired Heating Systems)

A technician is measuring draft in the flue of an oil-fired appliance. Which instrument is appropriate for this measurement?

  1. A hygrometer reading relative humidity
  2. A pyrometer reading surface temperature
  3. A volt-ohmmeter reading millivolts
  4. A manometer or draft gauge reading inches of water column Correct answer.

Explanation

Flue draft is a very small negative pressure, conventionally expressed in inches of water column and measured with a draft gauge or manometer. Other instruments measure unrelated properties such as humidity, voltage, or temperature.

Question 31Oil Heat (Oil-Fired Heating Systems)

What is the function of the barometric draft regulator installed in the flue connector of an oil appliance?

  1. It increases the firing rate of the nozzle
  2. It shuts off the burner when the flue overheats
  3. It stabilizes overfire draft by admitting room air into the flue Correct answer.
  4. It filters soot from the flue gases

Explanation

The barometric regulator opens to admit room air and relieve excess chimney draft, holding a steady overfire draft. Stable draft supports consistent combustion and prevents excess air from varying with weather.

Question 32Oil Heat (Oil-Fired Heating Systems)

A technician is checking the oil supply line to a burner. Which condition indicates that air is being drawn into the suction line?

  1. A slight rise in tank level overnight
  2. A steady, quiet oil flow at the bleeder
  3. A hard, sputtering sound at the bleeder with foamy oil Correct answer.
  4. A warm suction line near the tank

Explanation

Air entering the suction side of the pump produces sputtering and foam when the bleeder is opened. Foamy oil and erratic flame quality are classic signs of a suction leak.

Question 33Oil Heat (Oil-Fired Heating Systems)

Why is a fusible link or fire safety valve installed in the oil supply line at the tank?

  1. To preheat the oil before it reaches the nozzle
  2. To meter oil flow to the burner at a constant rate
  3. To stop oil flow if a fire occurs near the appliance Correct answer.
  4. To separate water from the fuel oil

Explanation

A fusible link valve closes on high temperature to shut off fuel at the tank and limit the fuel available to a fire. It is a safety device, not a metering or conditioning component.

Question 34Oil Heat (Oil-Fired Heating Systems)

A technician replaces a nozzle with one of the same GPH but a wider spray angle. What is the most likely effect if the original angle was matched to the chamber shape?

  1. The flame pattern may impinge on the chamber walls and increase soot Correct answer.
  2. The pump pressure will rise automatically
  3. The cad cell will lose sensitivity to flame
  4. The transformer output will increase

Explanation

Spray angle must match chamber geometry so the flame does not touch the walls, which cools combustion and produces soot. Changing to a wider angle can cause impingement and smoky operation.

Question 35Oil Heat (Oil-Fired Heating Systems)

A technician is setting up a burner on a boiler and reads a net stack temperature of 500°F with 12 percent CO2. If the appliance is clean and the draft is correct, what does the elevated net stack temperature most likely suggest?

  1. A plugged or restricted flue passage Correct answer.
  2. Undersized nozzle and low firing rate
  3. A boiler with a high heat-exchange efficiency
  4. Excessive excess air in the combustion zone

Explanation

A restricted flue reduces heat transfer to the water and raises stack temperature, lowering efficiency. Net stack temperature is corrected for room temperature and compared against the appliance chart, and elevated values suggest fouling or restriction.

Question 36Oil Heat (Oil-Fired Heating Systems)

A technician is converting a burner from a hollow-cone to a solid-cone nozzle of the same GPH and angle. What should be verified first?

  1. That the combustion chamber and air pattern suit the solid spray pattern Correct answer.
  2. That the pump pressure can be lowered to 50 psi
  3. That the flue is sealed to prevent air entry
  4. That the cad cell is removed during startup

Explanation

Hollow- and solid-cone nozzles distribute oil differently and require compatible chamber and air patterns. The manufacturer's approved combinations must be followed to avoid impingement and poor combustion.

Question 37Oil Heat (Oil-Fired Heating Systems)

A technician is diagnosing a burner that starts, flames, and then shuts down after about 30 seconds with the cad cell wiring disconnected. Which conclusion is correct?

  1. The burner should run until the thermostat is satisfied
  2. The burner should short-cycle on the high limit
  3. The burner should run normally because the cad cell is only a backup
  4. The burner should lock out because the control cannot prove flame Correct answer.

Explanation

The cad cell is the primary flame-proving device on modern burners. With it disconnected the control sees no flame and goes to lockout after the trial-for-ignition period.

Question 38Oil Heat (Oil-Fired Heating Systems)

A technician is installing a tank with a two-line supply. What is the function of the bypass plug in the fuel unit?

  1. It routes return oil internally so the pump can build pressure Correct answer.
  2. It limits maximum nozzle line pressure to 100 psi
  3. It prevents oil from entering the strainer
  4. It converts the pump from two-line to one-line operation

Explanation

In two-line service the bypass plug must be removed or installed per the pump manufacturer so excess oil returns to the tank rather than recirculating internally. Misconfiguration can cause seal failure or pressure problems.

Question 39Oil Heat (Oil-Fired Heating Systems)

A technician is checking a burner where the oil pump pressure gauge reads steady at 100 psi but the nozzle line pressure fluctuates. What is the most likely component to inspect?

  1. The ignition transformer secondary
  2. The barometric draft regulator
  3. The pressure regulating valve and its spring Correct answer.
  4. The cad cell mounting bracket

Explanation

Pump outlet pressure and nozzle line pressure should both be steady; fluctuation points to a worn regulating valve, spring, or pulsation in the pump. Electrical and draft components do not cause nozzle line pressure fluctuation.

Question 40Oil Heat (Oil-Fired Heating Systems)

A technician is diagnosing an oil burner that produces a rumbling, delayed ignition on every start. Which condition is the most likely cause?

  1. A thermostat set too low
  2. Oil accumulating in the chamber before ignition Correct answer.
  3. Excessive combustion air from a wide-open air shutter
  4. A cad cell that is too clean

Explanation

Delayed ignition occurs when oil is delivered and accumulates before the spark or flame ignites it, producing a rumble or puff. Causes include weak spark, wrong electrode setting, or delayed valve opening.

Question 41Oil Heat (Oil-Fired Heating Systems)

A technician is evaluating an oil-fired furnace with a heat exchanger that has developed cracks. What is the primary safety concern?

  1. Combustion products can enter the circulating air stream Correct answer.
  2. The draft regulator will close permanently
  3. The burner will fire at a higher rate
  4. The nozzle will clog more quickly

Explanation

A cracked heat exchanger allows flue gases, including carbon monoxide, to mix with supply air. This is a serious safety hazard and requires the appliance to be taken out of service.

Question 42Oil Heat (Oil-Fired Heating Systems)

A technician is tuning a burner and observes a CO2 reading of 13 percent with a smoke spot of 3. What is the appropriate next step?

  1. Leave the settings because high CO2 indicates peak efficiency
  2. Decrease excess air to raise CO2 further
  3. Increase excess air to reduce smoke while watching CO2 Correct answer.
  4. Increase pump pressure to richen the mixture

Explanation

A smoke spot of 3 is too high and indicates incomplete combustion even though CO2 is high. Opening the air shutter reduces smoke, though CO2 will fall slightly; the goal is the highest CO2 consistent with an acceptable smoke number.

Question 43Oil Heat (Oil-Fired Heating Systems)

A technician is verifying the operation of a primary control with a pre-purge and a post-purge feature. What does the post-purge accomplish?

  1. It reopens the oil valve to keep the nozzle warm
  2. It raises the chamber temperature for the next start
  3. It removes residual combustion gases and heat from the chamber after shutdown Correct answer.
  4. It resets the cad cell resistance

Explanation

Post-purge continues blower operation after the flame is extinguished to clear residual gases and reduce heat retention and odor. It supports cleaner shutdown and reduces sooting on restart.

Question 44Oil Heat (Oil-Fired Heating Systems)

A technician is testing a stack relay on an older burner. How does a stack relay detect that the flame is established?

  1. By sensing the light from the flame
  2. By sensing the temperature rise in the flue Correct answer.
  3. By measuring oil pressure at the pump
  4. By measuring the current in the transformer

Explanation

A stack relay uses a heat-sensitive element in the flue that responds to the temperature rise produced by a flame. It is a thermal flame-proving device, unlike the optical cad cell.

Question 45Oil Heat (Oil-Fired Heating Systems)

A technician is evaluating a tank installation where the tank outlet is above the burner. Which arrangement is typically acceptable for this elevation?

  1. A one-line gravity feed with the pump configured for single-line operation Correct answer.
  2. A system with the vent capped to hold pressure
  3. A two-line system with the return line above the oil level
  4. A system that requires a lift pump regardless of elevation

Explanation

When the tank is above the burner, gravity assists oil flow and a single-line system is commonly acceptable per manufacturer instructions. A two-line system is normally used when the tank is below the burner or the line is long.

Question 46Oil Heat (Oil-Fired Heating Systems)

A technician is diagnosing a burner that runs but the boiler never reaches setpoint, and the technician finds the nozzle is partially plugged. What is the expected combustion effect?

  1. Increased draft with lower CO2
  2. No change in firing rate but higher stack temperature
  3. Higher firing rate with a richer mixture
  4. Reduced firing rate with a leaner mixture and possible flame instability Correct answer.

Explanation

A partially plugged nozzle reduces oil flow, lowering the firing rate and changing the air-fuel ratio toward lean. The flame may become unstable and the appliance may not keep up with load.

Question 47Oil Heat (Oil-Fired Heating Systems)

A technician is measuring the electrode gap on a burner and finds it set to 1/8 inch. Which problem is most likely if the gap is too wide?

  1. The cad cell will read a lower resistance
  2. The nozzle will deliver more oil
  3. The spark may be weak or intermittent, causing delayed ignition Correct answer.
  4. The transformer will overheat and fail immediately

Explanation

A gap that is too wide raises the voltage needed to jump the gap and may produce a weak or intermittent spark, leading to delayed ignition. Manufacturer specifications for gap and position must be followed.

Question 48Oil Heat (Oil-Fired Heating Systems)

A technician is commissioning an oil-fired boiler and must verify the draft is stable. Which reading indicates a proper negative overfire draft?

  1. A positive pressure of 0.05 inches of water column in the chamber
  2. A negative pressure of about 0.02 inches of water column in the chamber Correct answer.
  3. A negative pressure of 2.0 inches of water column in the chamber
  4. A zero reading in the chamber with a positive flue pressure

Explanation

Oil-fired appliances are typically set for a slight negative overfire draft, commonly around -0.02 inches of water column, with the flue draft adjusted by the barometric regulator. Excessive negative draft or positive pressure indicates a venting or regulator problem.

Question 49Oil Heat (Oil-Fired Heating Systems)

A technician is analyzing a burner that produces a heavy smoke spot with low CO2 and a lazy orange flame. Which correction is most appropriate?

  1. Increase pump pressure to improve atomization
  2. Advance the cad cell closer to the flame
  3. Increase combustion air and check for a blocked air passage Correct answer.
  4. Reduce combustion air to raise CO2

Explanation

Heavy smoke with low CO2 and a lazy flame indicates insufficient air or poor mixing, so air delivery should be increased and obstructions cleared. Once air is adequate, the fuel side can be evaluated for atomization issues.

Question 50Oil Heat (Oil-Fired Heating Systems)

A technician is evaluating a two-line oil system where the return line runs back to the tank. What is the primary reason the return line is terminated below the oil level?

  1. To allow the tank to be filled from the return line
  2. To increase the pump discharge pressure
  3. To prevent air from being drawn into the pump through the return Correct answer.
  4. To reduce the nozzle flow rate

Explanation

Terminating the return below the oil level keeps the return line flooded and prevents air from being drawn back into the pump. Air in the return can cause erratic operation and loss of prime.