NYC CUSTODIAN ENGINEER PRACTICE TEST QUESTIONS|
REAL EXAM CURRENTLY TESTING ACTUAL QUESTIONS AND
VERIFIED ANSWERS EXPERT VERIFIED FOR GUARANTEED
PASS 2026
SECTION 1: BOILER OPERATIONS – LOW AND HIGH PRESSURE (Questions 1–45)
1. According to the NYC Mechanical Code, what is the maximum allowable
pressure for a boiler to be legally classified and operated as a
"low-pressure" steam boiler?
A) 5 psi
B) 15 psi
C) 100 psi
D) 150 psi
Answer: B) 15 psi
Rationale: In NYC, any steam boiler operating above 15 psi is classified
as high-pressure and requires a different class of licensure and stricter
operating protocols. Low-pressure steam boilers are limited to 15 psig.
2. What is the primary function of the "Hartford Loop" in a steam heating
system found in many older New York City public school buildings?
A) To increase the velocity of steam as it travels to the furthest radiator
B) To provide a bypass route for steam when the main header is closed
C) To prevent the boiler from losing its water level below a safe point in
the event of a leak in the return line
D) To trap air and vent it out of the system before it reaches the boiler
Answer: C) To prevent the boiler from losing its water level below a safe
point in the event of a leak in the return line
Rationale: The Hartford Loop is a safety piping arrangement that prevents
water from being siphoned out of the boiler if a return line breaks,
protecting the crown sheet from overheating.
1
,3. Which specific device is mandated by NYC code to shut off the fuel supply
to the burner if the water level in the boiler drops below the lowest safe
operating point?
A) The pressuretrol
B) The aqua-stat
C) The low-water cutoff (LWCO)
D) The OS&Y valve
Answer: C) The low-water cutoff (LWCO)
Rationale: The low-water cutoff (LWCO) is a safety device mandated by NYC
code to shut off the fuel supply to the burner if the water level drops
below the lowest safe operating point, preventing boiler damage or explosion.
4. A Custodian Engineer discovers that a low-pressure boiler is short-cycling
repeatedly during peak heating hours. What is the MOST appropriate first
action?
A) Replace the circulating pump immediately
B) Increase the thermostat setting throughout the building
C) Inspect the pressure control and operating controls
D) Shut down the boiler for the remainder of the day
Answer: C) Inspect the pressure control and operating controls
Rationale: Short-cycling is commonly caused by faulty pressure controls,
limit settings, or operating controls. Inspecting and verifying control
operation is the proper first troubleshooting step before replacing
components or shutting down equipment unnecessarily.
5. A Custodian Engineer notices a faint odor of natural gas in a school
boiler room. What is the FIRST course of action?
A) Locate the main gas shut-off valve and close it
B) Open all windows and doors to ventilate the area
C) Evacuate the area and call 911 from a remote location
2
, D) Attempt to locate the leak using a soapy water solution
Answer: C) Evacuate the area and call 911 from a remote location
Rationale: Any action that could create a spark, including using a phone
in the area or operating electrical switches, poses an ignition risk.
Evacuation and calling from a safe remote location is the mandated first
step per FDNY safety protocols.
6. What is the primary purpose of a boiler's safety valve?
A) To control the water temperature
B) To automatically release excess pressure and prevent boiler explosions
C) To regulate the fuel flow to the burner
D) To monitor the water level in the boiler
Answer: B) To automatically release excess pressure and prevent boiler
explosions
Rationale: Safety valves are critical pressure-relief devices that
automatically open when the boiler pressure exceeds the set point,
preventing catastrophic boiler failure.
7. If a Custodian Engineer observes "priming" or "foaming" in the boiler
sight glass, which of the following is the most likely cause and
appropriate corrective action?
A) Low water level; add more feedwater immediately
B) High concentration of dissolved solids or oil in the water; perform a
surface blowdown
C) Excessive oxygen in the system; add sodium sulfite
D) Scale buildup on the tubes; increase the dosage of phosphates
Answer: B) High concentration of dissolved solids or oil in the water;
perform a surface blowdown
Rationale: Foaming is caused by impurities on the surface of the water;
a surface blowdown removes these impurities to prevent water carryover
3
, into the steam lines.
8. What is the most common fuel used in steam boilers in NYC public buildings?
A) Gasoline
B) Natural gas
C) Diesel
D) Propane
Answer: B) Natural gas
Rationale: Natural gas is widely used for boilers due to its efficiency,
availability, and cost-effectiveness in NYC.
9. What is the primary purpose of a low-water cutoff on a steam boiler?
A) Increase steam pressure
B) Shut down the burner if the water level becomes unsafe
C) Improve fuel efficiency
D) Reduce condensate flow
Answer: B) Shut down the burner if the water level becomes unsafe
Rationale: The low-water cutoff is a safety device that shuts down the
burner when the water level in the boiler drops below a safe point,
preventing damage to the boiler from overheating.
10. What is the purpose of a boiler blowdown valve?
A) To reduce steam pressure
B) To remove sediment and dissolved solids from the boiler water
C) To test the safety valve
D) To increase boiler efficiency by lowering water temperature
Answer: B) To remove sediment and dissolved solids from the boiler water
Rationale: Blowdown removes impurities that accumulate at the bottom of
the boiler, preventing scale buildup and maintaining water quality.
4
REAL EXAM CURRENTLY TESTING ACTUAL QUESTIONS AND
VERIFIED ANSWERS EXPERT VERIFIED FOR GUARANTEED
PASS 2026
SECTION 1: BOILER OPERATIONS – LOW AND HIGH PRESSURE (Questions 1–45)
1. According to the NYC Mechanical Code, what is the maximum allowable
pressure for a boiler to be legally classified and operated as a
"low-pressure" steam boiler?
A) 5 psi
B) 15 psi
C) 100 psi
D) 150 psi
Answer: B) 15 psi
Rationale: In NYC, any steam boiler operating above 15 psi is classified
as high-pressure and requires a different class of licensure and stricter
operating protocols. Low-pressure steam boilers are limited to 15 psig.
2. What is the primary function of the "Hartford Loop" in a steam heating
system found in many older New York City public school buildings?
A) To increase the velocity of steam as it travels to the furthest radiator
B) To provide a bypass route for steam when the main header is closed
C) To prevent the boiler from losing its water level below a safe point in
the event of a leak in the return line
D) To trap air and vent it out of the system before it reaches the boiler
Answer: C) To prevent the boiler from losing its water level below a safe
point in the event of a leak in the return line
Rationale: The Hartford Loop is a safety piping arrangement that prevents
water from being siphoned out of the boiler if a return line breaks,
protecting the crown sheet from overheating.
1
,3. Which specific device is mandated by NYC code to shut off the fuel supply
to the burner if the water level in the boiler drops below the lowest safe
operating point?
A) The pressuretrol
B) The aqua-stat
C) The low-water cutoff (LWCO)
D) The OS&Y valve
Answer: C) The low-water cutoff (LWCO)
Rationale: The low-water cutoff (LWCO) is a safety device mandated by NYC
code to shut off the fuel supply to the burner if the water level drops
below the lowest safe operating point, preventing boiler damage or explosion.
4. A Custodian Engineer discovers that a low-pressure boiler is short-cycling
repeatedly during peak heating hours. What is the MOST appropriate first
action?
A) Replace the circulating pump immediately
B) Increase the thermostat setting throughout the building
C) Inspect the pressure control and operating controls
D) Shut down the boiler for the remainder of the day
Answer: C) Inspect the pressure control and operating controls
Rationale: Short-cycling is commonly caused by faulty pressure controls,
limit settings, or operating controls. Inspecting and verifying control
operation is the proper first troubleshooting step before replacing
components or shutting down equipment unnecessarily.
5. A Custodian Engineer notices a faint odor of natural gas in a school
boiler room. What is the FIRST course of action?
A) Locate the main gas shut-off valve and close it
B) Open all windows and doors to ventilate the area
C) Evacuate the area and call 911 from a remote location
2
, D) Attempt to locate the leak using a soapy water solution
Answer: C) Evacuate the area and call 911 from a remote location
Rationale: Any action that could create a spark, including using a phone
in the area or operating electrical switches, poses an ignition risk.
Evacuation and calling from a safe remote location is the mandated first
step per FDNY safety protocols.
6. What is the primary purpose of a boiler's safety valve?
A) To control the water temperature
B) To automatically release excess pressure and prevent boiler explosions
C) To regulate the fuel flow to the burner
D) To monitor the water level in the boiler
Answer: B) To automatically release excess pressure and prevent boiler
explosions
Rationale: Safety valves are critical pressure-relief devices that
automatically open when the boiler pressure exceeds the set point,
preventing catastrophic boiler failure.
7. If a Custodian Engineer observes "priming" or "foaming" in the boiler
sight glass, which of the following is the most likely cause and
appropriate corrective action?
A) Low water level; add more feedwater immediately
B) High concentration of dissolved solids or oil in the water; perform a
surface blowdown
C) Excessive oxygen in the system; add sodium sulfite
D) Scale buildup on the tubes; increase the dosage of phosphates
Answer: B) High concentration of dissolved solids or oil in the water;
perform a surface blowdown
Rationale: Foaming is caused by impurities on the surface of the water;
a surface blowdown removes these impurities to prevent water carryover
3
, into the steam lines.
8. What is the most common fuel used in steam boilers in NYC public buildings?
A) Gasoline
B) Natural gas
C) Diesel
D) Propane
Answer: B) Natural gas
Rationale: Natural gas is widely used for boilers due to its efficiency,
availability, and cost-effectiveness in NYC.
9. What is the primary purpose of a low-water cutoff on a steam boiler?
A) Increase steam pressure
B) Shut down the burner if the water level becomes unsafe
C) Improve fuel efficiency
D) Reduce condensate flow
Answer: B) Shut down the burner if the water level becomes unsafe
Rationale: The low-water cutoff is a safety device that shuts down the
burner when the water level in the boiler drops below a safe point,
preventing damage to the boiler from overheating.
10. What is the purpose of a boiler blowdown valve?
A) To reduce steam pressure
B) To remove sediment and dissolved solids from the boiler water
C) To test the safety valve
D) To increase boiler efficiency by lowering water temperature
Answer: B) To remove sediment and dissolved solids from the boiler water
Rationale: Blowdown removes impurities that accumulate at the bottom of
the boiler, preventing scale buildup and maintaining water quality.
4
