NYC Custodian Engineer Exam – Complete Civil Service Practice
Test Bank with Verified Answers & Technical Rationales | Newest
2026 Edition
Secure a top tier score on the highly competitive New York City Department of
Education civil service hiring roster with this definitive NYC Custodian Engineer exam
preparation guide. This comprehensive test bank features realistic practice questions
with verified correct answers and detailed technical rationales covering high-pressure
boiler operations, HVAC maintenance, structural building safety, electrical systems, and
administrative labor regulations. It is an indispensable resource for facility managers
and mechanical professionals looking to pass the DCAS examination on their very first
attempt.
1. A low-pressure steam boiler is operating at 12 psig and the safety valve begins
to simmer. The engineer notes that the burner continues to fire. What is the most
appropriate first action?
A. Immediately shut down the boiler
B. Verify the operating pressure control setting against the actual gauge reading
C. Open the blowdown valve to reduce pressure
D. Increase the feedwater flow
Rationale: A safety valve simmering at a pressure below its set point may indicate a faulty
pressure control or gauge. The engineer should verify the control setting and pressure
gauge accuracy before taking further action. Shutting down immediately without
assessment is premature.
2. A heating system uses a two-pipe steam system. Which statement correctly
describes the function of the return pipe?
A. It supplies steam to the radiators
B. It carries condensate back to the boiler
C. It equalizes pressure between supply and return
D. It vents air from the system
Rationale: In a two-pipe steam system, one pipe supplies steam to the radiators, and the
other pipe carries condensate and air back to the boiler or to a condensate receiver.
,Understanding the return piping is essential for troubleshooting water hammer or slow
heating issues.
3. A custodian engineer notices that a radiators in a steam heating system are not
heating evenly—some are hot, others are cold. What is the most likely cause?
A. Low water level in the boiler
B. Air trapped in the system or malfunctioning steam traps
C. High steam pressure
D. Insufficient fuel supply
Rationale: Uneven heating in a steam system is often caused by air binding (air trapped in
radiators) or faulty steam traps that fail to allow condensate to return, preventing steam
from entering the radiator. The system may need to be vented, and traps may require
inspection or replacement.
4. What is the primary purpose of a "drip leg" or "sediment trap" on a gas piping
system?
A. To increase gas pressure
B. To collect condensate and debris before they enter the gas control valve
C. To regulate gas flow
D. To shut off gas flow in an emergency
Rationale: A drip leg or sediment trap is installed in gas piping to catch any moisture, dirt,
or debris present in the gas before it reaches the control valve, burner, or other sensitive
components. Proper installation and periodic cleaning are necessary to maintain
equipment reliability.
5. A building engineer suspects scale buildup inside a boiler. Which of the
following is a common indicator of scale formation?
A. Increased fuel consumption to maintain operating pressure
B. Decreased stack temperature
,C. Lower water level in the sight glass
D. Increased feedwater temperature
Rationale: Scale acts as an insulator, reducing heat transfer from the hot gases to the
water. As a result, the boiler must fire longer and use more fuel to generate the same
amount of steam. Stack temperature may also increase, and tube overheating can occur.
Monitoring fuel consumption and boiler efficiency helps identify scale-related issues.
6. When operating a hot water heating boiler, what is the function of an expansion
tank?
A. To supply makeup water to the system
B. To accommodate the increase in water volume as temperature rises
C. To circulate water through the system
D. To regulate the temperature of the water
Rationale: As water in a hot water heating system is heated, it expands in volume. The
expansion tank provides a space for the expanded water to go, preventing excessive
pressure buildup in the system. Proper sizing and maintenance of the expansion tank are
important for system safety.
7. A building engineer is troubleshooting a hot water heating system that is not
producing heat. The circulator pump is running, the boiler is firing, but return
water temperature is very low. What is the most likely cause?
A. The boiler is short-cycling
B. Air is trapped in the system or the flow is obstructed
C. The pump is installed backwards
D. The thermostats are set too low
Rationale: The boiler is producing heat, but the heat is not reaching the radiators or the
return water is cold. This indicates a circulation problem, often due to trapped air (which
can cause an air lock) or a blockage in the piping, valves, or strainer. Checking for air in
the system and bleeding radiators would be an appropriate step.
, 8. A chilled water system is experiencing low delta T (the difference between
supply and return water temperature). What does this indicate?
A. The chiller is operating efficiently
B. There is a flow problem or the chiller is not removing enough heat
C. The condenser water temperature is too low
D. The refrigerant charge is low
Rationale: Low delta T indicates that the return water is not warm enough relative to the
chilled water supply. This means the system is not removing heat effectively, often due to
insufficient airflow over cooling coils, dirty coils, or improper flow. This condition can lead
to chiller inefficiency and reduced cooling capacity.
9. A variable air volume (VAV) system supplies 55°F air to a building. During a hot
summer day, the VAV boxes throughout the building are at maximum airflow, but
the space temperature is 75°F. What is the most likely cause?
A. The chilled water temperature is too low
B. The supply air temperature setpoint is too high or the cooling capacity is
insufficient
C. The VAV box minimum flow settings are incorrect
D. The thermostats are set to heating mode
Rationale: If the VAV boxes are at maximum flow, the system is providing all the cooling it
can. The space temperature of 75°F indicates that the cooling capacity is insufficient. The
most likely cause is that the supply air temperature is too high (above 55°F), or the chiller
is not producing enough cooling capacity to meet the load. Checking the supply air
temperature and chiller operation is a good first step.
10. A building engineer observes that a cooling tower is not producing the
expected temperature drop across the tower. Which of the following is the most
common cause?
A. Low ambient temperature
B. Inadequate water flow or airflow through the tower
C. The water is too cold
D. The condenser water pump is oversized
Test Bank with Verified Answers & Technical Rationales | Newest
2026 Edition
Secure a top tier score on the highly competitive New York City Department of
Education civil service hiring roster with this definitive NYC Custodian Engineer exam
preparation guide. This comprehensive test bank features realistic practice questions
with verified correct answers and detailed technical rationales covering high-pressure
boiler operations, HVAC maintenance, structural building safety, electrical systems, and
administrative labor regulations. It is an indispensable resource for facility managers
and mechanical professionals looking to pass the DCAS examination on their very first
attempt.
1. A low-pressure steam boiler is operating at 12 psig and the safety valve begins
to simmer. The engineer notes that the burner continues to fire. What is the most
appropriate first action?
A. Immediately shut down the boiler
B. Verify the operating pressure control setting against the actual gauge reading
C. Open the blowdown valve to reduce pressure
D. Increase the feedwater flow
Rationale: A safety valve simmering at a pressure below its set point may indicate a faulty
pressure control or gauge. The engineer should verify the control setting and pressure
gauge accuracy before taking further action. Shutting down immediately without
assessment is premature.
2. A heating system uses a two-pipe steam system. Which statement correctly
describes the function of the return pipe?
A. It supplies steam to the radiators
B. It carries condensate back to the boiler
C. It equalizes pressure between supply and return
D. It vents air from the system
Rationale: In a two-pipe steam system, one pipe supplies steam to the radiators, and the
other pipe carries condensate and air back to the boiler or to a condensate receiver.
,Understanding the return piping is essential for troubleshooting water hammer or slow
heating issues.
3. A custodian engineer notices that a radiators in a steam heating system are not
heating evenly—some are hot, others are cold. What is the most likely cause?
A. Low water level in the boiler
B. Air trapped in the system or malfunctioning steam traps
C. High steam pressure
D. Insufficient fuel supply
Rationale: Uneven heating in a steam system is often caused by air binding (air trapped in
radiators) or faulty steam traps that fail to allow condensate to return, preventing steam
from entering the radiator. The system may need to be vented, and traps may require
inspection or replacement.
4. What is the primary purpose of a "drip leg" or "sediment trap" on a gas piping
system?
A. To increase gas pressure
B. To collect condensate and debris before they enter the gas control valve
C. To regulate gas flow
D. To shut off gas flow in an emergency
Rationale: A drip leg or sediment trap is installed in gas piping to catch any moisture, dirt,
or debris present in the gas before it reaches the control valve, burner, or other sensitive
components. Proper installation and periodic cleaning are necessary to maintain
equipment reliability.
5. A building engineer suspects scale buildup inside a boiler. Which of the
following is a common indicator of scale formation?
A. Increased fuel consumption to maintain operating pressure
B. Decreased stack temperature
,C. Lower water level in the sight glass
D. Increased feedwater temperature
Rationale: Scale acts as an insulator, reducing heat transfer from the hot gases to the
water. As a result, the boiler must fire longer and use more fuel to generate the same
amount of steam. Stack temperature may also increase, and tube overheating can occur.
Monitoring fuel consumption and boiler efficiency helps identify scale-related issues.
6. When operating a hot water heating boiler, what is the function of an expansion
tank?
A. To supply makeup water to the system
B. To accommodate the increase in water volume as temperature rises
C. To circulate water through the system
D. To regulate the temperature of the water
Rationale: As water in a hot water heating system is heated, it expands in volume. The
expansion tank provides a space for the expanded water to go, preventing excessive
pressure buildup in the system. Proper sizing and maintenance of the expansion tank are
important for system safety.
7. A building engineer is troubleshooting a hot water heating system that is not
producing heat. The circulator pump is running, the boiler is firing, but return
water temperature is very low. What is the most likely cause?
A. The boiler is short-cycling
B. Air is trapped in the system or the flow is obstructed
C. The pump is installed backwards
D. The thermostats are set too low
Rationale: The boiler is producing heat, but the heat is not reaching the radiators or the
return water is cold. This indicates a circulation problem, often due to trapped air (which
can cause an air lock) or a blockage in the piping, valves, or strainer. Checking for air in
the system and bleeding radiators would be an appropriate step.
, 8. A chilled water system is experiencing low delta T (the difference between
supply and return water temperature). What does this indicate?
A. The chiller is operating efficiently
B. There is a flow problem or the chiller is not removing enough heat
C. The condenser water temperature is too low
D. The refrigerant charge is low
Rationale: Low delta T indicates that the return water is not warm enough relative to the
chilled water supply. This means the system is not removing heat effectively, often due to
insufficient airflow over cooling coils, dirty coils, or improper flow. This condition can lead
to chiller inefficiency and reduced cooling capacity.
9. A variable air volume (VAV) system supplies 55°F air to a building. During a hot
summer day, the VAV boxes throughout the building are at maximum airflow, but
the space temperature is 75°F. What is the most likely cause?
A. The chilled water temperature is too low
B. The supply air temperature setpoint is too high or the cooling capacity is
insufficient
C. The VAV box minimum flow settings are incorrect
D. The thermostats are set to heating mode
Rationale: If the VAV boxes are at maximum flow, the system is providing all the cooling it
can. The space temperature of 75°F indicates that the cooling capacity is insufficient. The
most likely cause is that the supply air temperature is too high (above 55°F), or the chiller
is not producing enough cooling capacity to meet the load. Checking the supply air
temperature and chiller operation is a good first step.
10. A building engineer observes that a cooling tower is not producing the
expected temperature drop across the tower. Which of the following is the most
common cause?
A. Low ambient temperature
B. Inadequate water flow or airflow through the tower
C. The water is too cold
D. The condenser water pump is oversized
