Building & Utility Equipment Troubleshooting Q&A

Building Utility Equipment Troubleshooting — real-world interview & field troubleshooting questions with clear, practical answers. Tap any question to open its answer.

Showing the first 70 questions free. The complete 150-question set is available as a PDF below.

HVAC, AHU & Ventilation

Q1The HVAC system is running but rooms are not reaching the set temperature. How would you troubleshoot it?

AnswerCheck thermostat/setpoint, temperature sensors, chilled-water or refrigerant conditions, airflow, filters, dampers and fan operation. Compare supply and return temperatures; correct low flow, dirty filters, sensor error or control settings before checking major components.

Q2An AHU has very low airflow even though the fan is running. What should you inspect?

AnswerInspect dirty filters, closed dampers, blocked ducts, fan rotation, belt condition and fan speed. Measure differential pressure across filters and verify the VFD or motor is receiving the correct command.

Q3The supply-air temperature fluctuates continuously. What could be causing it?

AnswerCheck unstable chilled-water flow, hunting control valve, faulty temperature sensor, changing airflow or incorrect PID settings. Trend the sensor and valve position through the BMS to identify whether the instability is from measurement or control.

Q4An AHU fan trips after running for several minutes. How will you isolate the fault?

AnswerCheck motor current, overload setting, bearing condition, belt tension, filter pressure and fan rotation. If current rises gradually, look for mechanical load or restricted airflow; if the trip is electrical, inspect the motor, starter or VFD fault history.

Q5The ventilation fan produces excessive vibration. What should you check first?

AnswerInspect fan balance, bearing condition, shaft alignment, loose foundation bolts and belt or coupling condition. Check for debris on the impeller and correct the mechanical cause before changing speed settings.

Q6The exhaust fan rotates in the wrong direction after maintenance. How would you troubleshoot it?

AnswerFirst isolate power and verify the fan wiring and motor rotation against the required airflow direction. For a three-phase motor, correct the phase sequence according to the approved electrical procedure and then confirm airflow and current.

Q7A room has poor ventilation although the fan is operating normally. What would you investigate?

AnswerCheck fresh-air damper position, blocked intake/exhaust paths, duct restrictions, fan capacity and pressure balance. Also verify that the BMS command and actual damper position match.

Q8The AHU coil is freezing during cooling operation. How can you troubleshoot it?

AnswerCheck low airflow, dirty filter, insufficient fan speed, low chilled-water temperature, faulty freeze-stat and control-valve position. Restore adequate airflow and verify the freeze protection sequence before restarting the coil.

Q9The thermostat shows a normal reading but occupants complain that the room is hot. What should you verify?

AnswerCompare the thermostat reading with a calibrated reference instrument at the same location. Check sensor placement, supply-air temperature, airflow, heat load and whether the thermostat is affected by a nearby heat source.

Q10A ventilation system becomes noisy after maintenance. What should you inspect?

AnswerCheck loose access panels, fan guards, bolts, belts, bearings and duct connections that may have been disturbed during maintenance. Run the fan at normal speed and identify whether the noise follows the fan, duct or motor.

Chiller, Cooling Tower & Heat Rejection

Q11A chiller starts but shuts down on low-flow protection. What should you check?

AnswerVerify chilled-water pump operation, valve positions, flow switch status, strainer condition and differential pressure. Remove air or blockage and confirm actual flow before resetting the chiller protection.

Q12Chilled-water supply temperature is higher than normal even at full load. How will you diagnose it?

AnswerCheck condenser and evaporator temperatures, refrigerant condition, water flow, fouling and compressor loading. Compare operating pressures with the manufacturer range and determine whether the limitation is heat transfer, flow or refrigeration capacity.

Q13The cooling-tower fan is running but condenser-water temperature remains high. What could be wrong?

AnswerCheck airflow direction, fan speed, fill condition, spray nozzles, water distribution and condenser-water flow. Clean fouled fill/nozzles and verify fan pitch or VFD command if the tower cannot reject the required heat.

Q14A chiller shows high condenser pressure. How would you troubleshoot it?

AnswerCheck condenser-water temperature and flow, cooling-tower performance, condenser fouling and non-condensable conditions. Correct restricted flow or poor heat rejection first, then confirm pressure returns to the normal operating range.

Q15The cooling tower basin level keeps falling during operation. What should you inspect?

AnswerCheck make-up water control, overflow, blowdown setting, visible leaks and drift losses. Confirm the level sensor or float valve is functioning correctly before changing water-control settings.

Q16The cooling-tower fan trips on overload. What checks can identify the cause?

AnswerMeasure motor current and inspect fan blades, gearbox, bearings and belt condition for excessive mechanical load. Also verify fan speed, pitch and motor overload settings against the approved operating values.

Q17A chiller has frequent short cycling. What should you investigate?

AnswerCheck load demand, chilled-water volume, setpoint differential, flow switch operation and control sequence. A very small load or incorrect control differential can cause repeated starts, so correct the control strategy rather than repeatedly resetting the unit.

Q18The condenser-water pump runs but differential pressure is low. What could cause this?

AnswerCheck pump rotation, suction conditions, strainer blockage, valve position, impeller condition and system leakage. Compare suction/discharge pressure with the pump curve to determine whether the problem is hydraulic restriction or pump performance.

Q19The chiller evaporator pressure is abnormally low. What would you inspect?

AnswerCheck chilled-water flow, refrigerant charge/conditions, expansion device operation and evaporator fouling. Review the alarm history and operating temperatures before deciding whether the fault is on the water side or refrigeration side.

Q20The cooling tower is overflowing during normal operation. How can you find the reason?

AnswerInspect make-up valve, float/level controller, overflow arrangement and control signal. Verify the actual basin level against the indicated level because a faulty sensor can command continuous make-up water.

Pumps, Motors & Water Circulation

Q21A circulation pump is running but there is no water flow. What should you check?

AnswerCheck suction valve, discharge valve, strainer, air lock, pump rotation and impeller condition. Verify that the pump is properly primed and that suction pressure is adequate before dismantling the pump.

Q22A pump is delivering low flow compared with normal operation. How will you diagnose it?

AnswerMeasure suction and discharge pressure and compare them with the normal operating point. Inspect clogged strainers, partially closed valves, worn impeller, incorrect rotation and system restrictions.

Q23A pump motor draws high current after a recent piping change. What could be happening?

AnswerCheck discharge pressure, valve position, pump operating point, alignment and motor condition. A piping change can increase system flow or head and overload the pump, so compare actual duty with the pump curve before adjusting the motor.

Q24The pump is making a rattling sound and flow is unstable. What should you inspect?

AnswerCheck for cavitation by reviewing suction pressure, liquid temperature, suction blockage and NPSH conditions. Also inspect the impeller for damage and ensure the suction line is not drawing air.

Q25A water pump seal is leaking repeatedly after replacement. How would you troubleshoot it?

AnswerCheck shaft condition, alignment, seal installation, pump vibration, dry running and operating pressure. Replacing the seal again without correcting shaft runout, misalignment or dry-running conditions will usually cause another failure.

Q26The pump bearing temperature is rising. What should you check?

AnswerInspect lubrication quantity and grade, bearing condition, shaft alignment, coupling condition and vibration. Compare the temperature trend with normal values and stop the equipment if the bearing shows rapid overheating or abnormal noise.

Q27A standby pump fails to start automatically. What would you check?

AnswerVerify auto mode, duty/standby logic, level or pressure demand, start permissives and starter/VFD health. Check whether the controller is issuing a start command and whether an interlock is blocking it.

Q28The pump loses prime after every shutdown. How would you systematically locate the cause?

AnswerInspect foot/check valve, suction-line joints, air leakage and tank level. A small suction-side air leak may not show water leakage but can allow the pump to lose prime, so test the suction system carefully.

Q29Two pumps operate together but the flow does not increase as expected. What should you investigate?

AnswerCheck whether both pumps rotate correctly, whether both suction/discharge paths are open and whether their controls are coordinated. Verify pump curves and system resistance because parallel operation does not always produce double the flow.

Q30A pump repeatedly trips on overload only at high demand. What checks are useful?

AnswerMeasure motor current at different flow conditions and compare it with the motor rating and pump curve. Check for excessive flow, high system density, mechanical rubbing, bearing problems or incorrect impeller size.

Boiler, Steam & Hot Water

Q31A boiler fails to start when there is a heat demand. How would you troubleshoot it?

AnswerCheck fuel availability, burner permissives, water level, pressure controls, ignition sequence and safety interlocks. Read the burner/controller fault code and correct the failed permissive before attempting another start.

Q32The boiler starts but flame is lost after ignition. What should you inspect?

AnswerCheck fuel pressure, ignition quality, flame sensor signal, combustion air and burner adjustment. If the flame is present but the controller does not detect it, inspect the flame sensor and its wiring rather than repeatedly resetting the burner.

Q33Steam pressure is lower than the normal operating value. What could be causing it?

AnswerCheck burner firing rate, fuel supply, boiler water level, steam demand, heat-transfer-surface fouling and control settings. Compare pressure trend with load demand to determine whether the boiler is under-firing or the process demand has increased.

Q34The boiler pressure rises too quickly. What should you check?

AnswerVerify pressure-control settings, burner modulation, steam demand and pressure sensor accuracy. Check that the control valve or burner is not stuck at a high firing rate and confirm all safety controls are functional.

Q35Hot-water temperature is unstable in a building heating system. How will you isolate the problem?

AnswerCheck boiler modulation, mixing/control valve operation, circulation flow and temperature-sensor accuracy. Trend supply and return temperatures to determine whether the instability originates from the heat source or distribution system.

Q36The burner produces abnormal noise during firing. What should you inspect?

AnswerCheck combustion air, fuel pressure, burner nozzle condition, fan operation and burner alignment. Do not simply increase fuel or air; first identify whether the noise is caused by unstable combustion or a mechanical issue.

Q37A steam trap appears to discharge continuously. What would you check?

AnswerCheck whether the trap is stuck open, incorrectly sized, damaged or receiving abnormal condensate conditions. Compare upstream and downstream temperatures and follow the site testing procedure before replacing the trap.

Q38Boiler feedwater pump runs but feedwater pressure is insufficient. What should you inspect?

AnswerCheck suction conditions, pump rotation, suction strainer, discharge valve, impeller condition and pump speed. Confirm that the pump is not cavitating and compare measured pressure with the required boiler feedwater pressure.

Q39The boiler shows repeated low-water alarms even though the gauge glass looks normal. How can you investigate it?

AnswerCompare the level indication with an independent level reference and inspect level-sensor wiring, impulse lines and controller calibration. Check whether the alarm is real or caused by a faulty sensing system before changing the level setpoint.

Q40A hot-water circulation system takes too long to heat distant rooms. What should you check?

AnswerCheck circulation pump flow, balancing valves, air in the circuit, insulation and control-valve operation. Measure supply and return temperatures at multiple points to find where the heat distribution is being restricted.

Compressed Air & Utility Air

Q41Compressed-air pressure drops whenever production demand increases. How will you troubleshoot it?

AnswerCheck compressor capacity, receiver pressure, pressure drop across filters, dryer condition and major air leaks. Measure pressure at the compressor, main header and point of use to locate where the pressure loss occurs.

Q42The compressor runs continuously but the receiver never reaches set pressure. What should you inspect?

AnswerCheck inlet filter, unloading system, compressor capacity, discharge pressure and leakage rate. A large air leak or faulty unloader can keep the compressor loaded continuously, so compare loaded and unloaded behavior.

Q43Compressed air contains excessive water at the point of use. What should you check?

AnswerInspect aftercooler drainage, moisture separator, air dryer operation, drain traps and pipe slope. Check dew-point performance and confirm that automatic drains are not blocked or stuck closed.

Q44A pneumatic utility line has low pressure only at one area. How can you isolate the issue?

AnswerMeasure pressure upstream and downstream of filters, regulators, valves and flexible hoses in that branch. A partially closed valve, blocked filter or undersized hose can create a local pressure drop even when the main header pressure is normal.

Q45The air dryer shows normal operation but moisture is still reaching the plant. What would you investigate?

AnswerCheck dryer inlet conditions, dew point, bypass valve position, drains and downstream piping. Verify the dryer capacity is suitable for the actual air flow and temperature rather than relying only on the status display.

Q46The compressor motor trips on overload during hot weather. What could be causing it?

AnswerCheck ambient temperature, ventilation, compressor discharge pressure, cooling system, oil condition and motor current. High ambient temperature can reduce cooling performance, so correct ventilation and cooling before changing overload settings.

Q47Air pressure fluctuates rapidly near a regulator. What should you inspect?

AnswerCheck regulator sizing, inlet pressure stability, downstream demand and filter blockage. Verify the regulator sensing port is clean and that the regulator is not hunting because of an unsuitable setting or damaged diaphragm.

Q48The compressor makes unusual knocking noise. How should you approach the fault?

AnswerCheck oil level/condition, bearings, valves, mounting and abnormal vibration according to the compressor type and OEM procedure. Stop the machine if the noise is severe and investigate mechanically before returning it to service.

Q49An automatic condensate drain does not discharge water. What would you check?

AnswerCheck drain power, timer/level sensor, inlet blockage and the drain valve itself. Test the drain manually if permitted and clean the strainer or replace the valve if it is stuck.

Q50A compressed-air leak is suspected but cannot be heard. How can you locate it?

AnswerInspect fittings, hoses, valves and machine connections using an approved leak-detection method such as ultrasonic detection or pressure-decay testing. Repair the leak and then repeat the test to confirm the loss has reduced.

DG Set, Generator & Fuel System

Q51A DG set does not start automatically when mains power fails. What should you check?

AnswerCheck AMF/ATS mode, start permissives, battery voltage, fuel level, emergency-stop status and controller alarms. Verify whether the controller is sending a crank command and whether any interlock is blocking the start.

Q52The DG cranks but does not fire. How will you troubleshoot it?

AnswerCheck fuel level, fuel shutoff, priming, fuel filters, air in the fuel line and engine starting speed. Review the engine controller for fault codes and confirm that the stop solenoid or actuator is not preventing fuel delivery.

Q53The DG starts but stops after a short time. What should you inspect?

AnswerCheck low oil pressure, high coolant temperature, overspeed, fuel supply and controller protection alarms. Identify the exact shutdown cause from the controller before resetting the set.

Q54Generator output voltage is low under load. What could be the cause?

AnswerCheck engine speed/frequency, AVR operation, excitation circuit, terminal connections and load balance. Compare no-load and loaded voltage to determine whether the issue is excitation, speed or excessive voltage drop.

Q55DG frequency falls significantly when a large load starts. How would you investigate it?

AnswerCheck engine response, governor setting, fuel system, air filter and the magnitude of the connected load. Verify whether the load step is within generator capacity and whether other loads should be sequenced instead of starting together.

Q56The DG battery repeatedly becomes discharged. What should you check?

AnswerInspect battery condition, charger output, terminal connections and parasitic loads. Check whether the DG is being left in a condition where the battery charger is isolated or whether frequent unsuccessful starts are draining the battery.

Q57Engine coolant temperature is high during extended operation. What should you inspect?

AnswerCheck coolant level, radiator cleanliness, fan/belt condition, thermostat, water pump and airflow through the radiator. Confirm load percentage and ambient temperature because overheating may result from both cooling restrictions and excessive load.

Q58Black smoke increases when the DG is loaded. How would you troubleshoot it?

AnswerCheck air-filter restriction, turbocharger/air-intake condition, injector/fuel quality and engine loading. Compare smoke behavior with load and inspect the air system before making fuel adjustments.

Q59The generator trips when a motor starts. What should you investigate?

AnswerCheck motor starting current, generator capacity, voltage dip, protection settings and starting method of the motor. Reduce the starting impact through approved sequencing or a suitable starter/VFD if the generator is otherwise healthy.

Q60Fuel consumption of the DG has increased without a change in load. What checks are useful?

AnswerCheck engine load, fuel leakage, air-filter restriction, injector condition, coolant temperature and maintenance condition. Compare fuel rate with historical operating data at the same load to identify a real efficiency change.

Electrical Distribution, UPS & Emergency Power

Q61A building utility panel trips repeatedly after a new load is connected. How would you diagnose it?

AnswerCheck load current on each phase, breaker rating, cable size, short-circuit signs and the connected equipment for abnormal current. Determine whether the trip is overload, earth fault or short circuit before replacing the breaker.

Q62An emergency lighting circuit does not operate during a power failure. What should you check?

AnswerCheck emergency supply, battery/UPS status, charger, transfer function and circuit protection. Test the system under an approved simulated mains-failure condition and confirm that the emergency lights receive the expected supply.

Q63A UPS carries the load but its battery backup time is very short. What could be wrong?

AnswerCheck battery age, terminal voltage, charger performance, load percentage and battery temperature. Perform an approved battery test and compare actual capacity with the expected backup requirement before replacing the UPS.

Q64A UPS transfers to bypass unexpectedly. How would you troubleshoot it?

AnswerReview UPS alarms, input/output conditions, overload status, bypass supply quality and internal fault history. Confirm whether the transfer was caused by overload, inverter protection or an unstable input rather than treating it as a simple reset issue.

Q65One phase of a three-phase utility supply has noticeably higher current. What should you inspect?

AnswerMeasure phase currents with the actual load operating and identify large single-phase loads or loose connections. Redistribute suitable loads and inspect terminals for heating or poor contact after isolating the circuit safely.

Q66A motor feeder becomes hot although the measured current is near normal. What could cause it?

AnswerInspect terminal tightness, cable lug condition, contact resistance and ventilation around the panel. A loose or oxidized connection can create local heating without a large increase in total current.

Q67A contactor chatters during operation. What should you check?

AnswerCheck control voltage, coil rating, auxiliary contacts, loose wiring and mechanical condition of the contactor. Measure the coil voltage while the chatter occurs to identify whether the problem is control-supply instability or the contactor itself.

Q68An MCB trips only after the equipment has been running for some time. How can you isolate the cause?

AnswerMeasure operating current and observe whether the trip follows heating, overload or a particular operating cycle. Inspect cable temperature, motor condition and breaker characteristics; do not simply fit a higher-rated breaker.

Q69The utility room has frequent voltage fluctuations. What would you investigate?

AnswerRecord voltage over time and correlate fluctuations with large motors, lifts, chillers or other heavy loads. Check incoming supply quality, transformer loading, loose connections and power-quality events before changing sensitive equipment settings.

Q70An automatic transfer switch does not return the load to mains after restoration. What should you check?

AnswerVerify mains voltage sensing, return-to-mains timer, ATS mode, control power and interlocks. Check the event log to see whether the return command was issued but mechanically or electrically blocked.

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