PC Troubleshooting & Diagnostics 2 — Questions and Answers
Question 1: A customer reports that their water heater produces hot water for only a few minutes before it turns cold. What is the MOST likely cause?
- Faulty dip tube allowing cold and hot water to mix (Correct answer)
- Undersized pressure relief valve
- Corroded anode rod
- Blocked vent flue
Correct answer: Faulty dip tube allowing cold and hot water to mix
A broken or missing dip tube allows incoming cold water to mix directly with hot water near the top of the tank, drastically reducing hot water supply time.
Question 2: A floor drain is emitting sewer gas odors intermittently. The FIRST diagnostic step should be to:
- Replace the drain trap entirely
- Pour water into the drain to refill the trap (Correct answer)
- Inspect the main sewer line with a camera
- Add chemical drain cleaner
Correct answer: Pour water into the drain to refill the trap
An evaporated P-trap is the most common cause of intermittent sewer gas odors from floor drains, and pouring water restores the water seal immediately.
Question 3: A pressure gauge on a well pump system reads normal when the pump is off but drops significantly when any fixture is opened. This indicates:
- Waterlogged pressure tank (Correct answer)
- Faulty check valve on the pump
- Undersized supply main
- High static water pressure
Correct answer: Waterlogged pressure tank
A waterlogged pressure tank has lost its air cushion, causing rapid pressure drop when water is drawn because the tank holds almost no reserve.
Question 4: A gas water heater pilot light keeps going out repeatedly. After relighting, it extinguishes within seconds. The MOST likely faulty component is the:
- Gas supply valve
- Thermocouple (Correct answer)
- Combustion air inlet
- Flue damper
Correct answer: Thermocouple
A defective thermocouple fails to sense the pilot flame and signals the gas valve to close, extinguishing the pilot within seconds of lighting.
Question 5: During a visual inspection, a plumber notices the cold water pipe at a water heater is warm to the touch when no hot water is being used. This condition is called:
- Thermal siphoning / convection loop (Correct answer)
- Cross-connection contamination
- Pressure fluctuation backflow
- Heat exchanger bypass
Correct answer: Thermal siphoning / convection loop
Thermal siphoning occurs when hot water naturally rises and circulates backward through cold supply lines due to convection when no check valve is present.
Question 6: A kitchen faucet drips from the spout when turned off. The faucet is a cartridge-type single-handle. The MOST likely cause is:
- Worn O-rings on the valve body
- Failed cartridge seals (Correct answer)
- Loose packing nut
- Cracked faucet body
Correct answer: Failed cartridge seals
In cartridge faucets, a worn or damaged cartridge with failed internal seals is the most common cause of dripping from the spout.
Question 7: A homeowner complains of banging noises in the pipes when the washing machine valve closes. This phenomenon is known as:
- Pipe resonance
- Water hammer (Correct answer)
- Cavitation
- Thermal expansion knock
Correct answer: Water hammer
Water hammer is caused by a sudden stop of fast-moving water creating a pressure shockwave that produces a loud banging noise in the pipes.
PC Troubleshooting & Diagnostics 2
A customer reports that their water heater produces hot water for only a few minutes before it turns cold.
What is the MOST likely cause?