NYC CUSTODIAN ENGINEER EXAM –MOST TESTED PRACTICE
QUESTIONS WITH VERIFIED ANSWERS AND RATIONALES | 2026-
2027 Edition | All 9 Core Domains Covered | DCAS Civil Service
Exam Prep | Instant Download PDF
Description:
This comprehensive practice exam covers all NYC Custodian Engineer exam domains:
Boiler Operations & Steam Systems; HVAC Systems & Refrigeration; Electrical Systems &
Motor Controls; Plumbing Systems & Sanitary Maintenance; Fire Protection & Life Safety;
Building Codes, Regulations & Compliance; Safety & OSHA Standards; Building
Maintenance & Facility Management; and Administrative Duties & Supervisory
Responsibilities. Each question includes a verified correct answer with a concise rationale
for effective study and retention. Based on the official DCAS exam blueprint and current
NYC Mechanical Code, Fire Code, and Building Code standards.
Domain 1: Boiler Operations & Steam Systems (Q1–40)
1. According to the New York City 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. 10 psi
C. 15 psi
D. 30 psi
Answer: C. 15 psi
Under the NYC Mechanical Code, a low-pressure steam boiler operates at a pressure not
exceeding 15 psi.
,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 steam pressure in the boiler
B. To prevent the boiler from running dry if the return line is broken
C. To circulate hot water through the heating system
D. To regulate the temperature of the steam
Answer: B. To prevent the boiler from running dry if the return line is broken
The Hartford Loop is a piping arrangement that maintains water level in the boiler even if the
return line leaks or breaks.
3. If a Custodian Engineer observes "priming" or "foaming" in the boiler sight glass, which of
the following is the most likely cause?
A. Low water level
B. High concentration of dissolved solids or oil in the water
C. Excessive oxygen in the system
D. Scale buildup on the tubes
Answer: B. High concentration of dissolved solids or oil in the water
Foaming is caused by impurities on the water surface; a surface blowdown removes these
impurities.
4. 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 pressurertrol
B. The aqua-stat
C. The low-water cutoff
D. The OS&Y valve
Answer: C. The low-water cutoff
The low-water cutoff is the most critical safety device, preventing a dry-fire condition that
could lead to a catastrophic boiler explosion.
5. In a fire-tube boiler:
A. Water passes through tubes surrounded by combustion gases
B. Combustion gases pass through tubes surrounded by water
C. Both water and gases flow through the same tubes
D. There are no tubes
Answer: B. Combustion gases pass through tubes surrounded by water
Fire-tube boilers have hot combustion gases passing through tubes surrounded by water.
6. In a water-tube boiler:
A. Combustion gases pass through tubes surrounded by water
B. Water passes through tubes surrounded by combustion gases
C. Both water and gases flow through the same tubes
D. There are no tubes
, Answer: B. Water passes through tubes surrounded by combustion gases
Water-tube boilers have water flowing through tubes surrounded by hot combustion gases.
7. The expansion tank in a hot water heating system is designed to:
A. Allow for expansion of water as it heats
B. Increase water pressure
C. Store hot water for later use
D. Reduce water temperature
Answer: A. Allow for expansion of water as it heats
As water heats, it expands; the expansion tank provides space for expanded water to
prevent pressure buildup.
8. What is the purpose of a safety valve on a steam boiler?
A. To regulate steam pressure during normal operation
B. To release pressure if it exceeds the maximum allowable working pressure
C. To add water to the boiler
D. To measure steam temperature
Answer: B. To release pressure if it exceeds the maximum allowable working
pressure
Safety valves are the final protection against overpressure and must be tested regularly.
QUESTIONS WITH VERIFIED ANSWERS AND RATIONALES | 2026-
2027 Edition | All 9 Core Domains Covered | DCAS Civil Service
Exam Prep | Instant Download PDF
Description:
This comprehensive practice exam covers all NYC Custodian Engineer exam domains:
Boiler Operations & Steam Systems; HVAC Systems & Refrigeration; Electrical Systems &
Motor Controls; Plumbing Systems & Sanitary Maintenance; Fire Protection & Life Safety;
Building Codes, Regulations & Compliance; Safety & OSHA Standards; Building
Maintenance & Facility Management; and Administrative Duties & Supervisory
Responsibilities. Each question includes a verified correct answer with a concise rationale
for effective study and retention. Based on the official DCAS exam blueprint and current
NYC Mechanical Code, Fire Code, and Building Code standards.
Domain 1: Boiler Operations & Steam Systems (Q1–40)
1. According to the New York City 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. 10 psi
C. 15 psi
D. 30 psi
Answer: C. 15 psi
Under the NYC Mechanical Code, a low-pressure steam boiler operates at a pressure not
exceeding 15 psi.
,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 steam pressure in the boiler
B. To prevent the boiler from running dry if the return line is broken
C. To circulate hot water through the heating system
D. To regulate the temperature of the steam
Answer: B. To prevent the boiler from running dry if the return line is broken
The Hartford Loop is a piping arrangement that maintains water level in the boiler even if the
return line leaks or breaks.
3. If a Custodian Engineer observes "priming" or "foaming" in the boiler sight glass, which of
the following is the most likely cause?
A. Low water level
B. High concentration of dissolved solids or oil in the water
C. Excessive oxygen in the system
D. Scale buildup on the tubes
Answer: B. High concentration of dissolved solids or oil in the water
Foaming is caused by impurities on the water surface; a surface blowdown removes these
impurities.
4. 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 pressurertrol
B. The aqua-stat
C. The low-water cutoff
D. The OS&Y valve
Answer: C. The low-water cutoff
The low-water cutoff is the most critical safety device, preventing a dry-fire condition that
could lead to a catastrophic boiler explosion.
5. In a fire-tube boiler:
A. Water passes through tubes surrounded by combustion gases
B. Combustion gases pass through tubes surrounded by water
C. Both water and gases flow through the same tubes
D. There are no tubes
Answer: B. Combustion gases pass through tubes surrounded by water
Fire-tube boilers have hot combustion gases passing through tubes surrounded by water.
6. In a water-tube boiler:
A. Combustion gases pass through tubes surrounded by water
B. Water passes through tubes surrounded by combustion gases
C. Both water and gases flow through the same tubes
D. There are no tubes
, Answer: B. Water passes through tubes surrounded by combustion gases
Water-tube boilers have water flowing through tubes surrounded by hot combustion gases.
7. The expansion tank in a hot water heating system is designed to:
A. Allow for expansion of water as it heats
B. Increase water pressure
C. Store hot water for later use
D. Reduce water temperature
Answer: A. Allow for expansion of water as it heats
As water heats, it expands; the expansion tank provides space for expanded water to
prevent pressure buildup.
8. What is the purpose of a safety valve on a steam boiler?
A. To regulate steam pressure during normal operation
B. To release pressure if it exceeds the maximum allowable working pressure
C. To add water to the boiler
D. To measure steam temperature
Answer: B. To release pressure if it exceeds the maximum allowable working
pressure
Safety valves are the final protection against overpressure and must be tested regularly.
