PC Troubleshooting & Diagnostics 3 — Questions and Answers
Question 1: A sump pump runs continuously but the pit water level keeps rising. After confirming the pump is running, the NEXT diagnostic step is to:
- Check the discharge line for an obstruction or siphon break issue (Correct answer)
- Replace the float switch
- Increase the pump motor voltage
- Inspect the pit for cracks
Correct answer: Check the discharge line for an obstruction or siphon break issue
If the pump runs but water rises, the discharge line may be blocked, kinked, or back-siphoning water into the pit, preventing effective pumping.
Question 2: A lavatory drain is slow even after the pop-up stopper mechanism has been cleaned. The MOST effective next step is to:
- Snake the drain through the overflow opening (Correct answer)
- Replace the P-trap
- Check and clear the fixture branch vent
- Pour hot water down the drain
Correct answer: Snake the drain through the overflow opening
Snaking through the overflow port directly accesses the drain line below the stopper, clearing blockages that surface cleaning cannot reach.
Question 3: A customer reports rust-colored water only when the hot water is first used in the morning. This MOST likely indicates:
- Corroding galvanized supply main
- Deteriorating anode rod inside the water heater tank (Correct answer)
- Cross-connection with a boiler system
- Sediment in the municipal supply
Correct answer: Deteriorating anode rod inside the water heater tank
A depleted anode rod allows the steel tank lining to corrode overnight, releasing rust particles that appear when hot water is first drawn.
Question 4: A toilet tank takes over five minutes to refill after flushing. The MOST likely cause is:
- Worn flapper causing continuous refill
- Partially closed or faulty fill valve (Correct answer)
- Undersized flush valve seat
- Cracked overflow tube
Correct answer: Partially closed or faulty fill valve
A partially closed supply stop or a clogged/faulty fill valve restricts water flow into the tank, dramatically increasing refill time.
Question 5: A plumber detects a drop in system pressure between two points in a supply line with no visible leaks. This is BEST described as:
- Pressure drop due to friction loss or a hidden restriction (Correct answer)
- Normal operating variance
- Thermal contraction of pipe
- Backpressure from a closed valve downstream
Correct answer: Pressure drop due to friction loss or a hidden restriction
A measurable pressure differential between two points with no obvious leak indicates friction loss from a partial blockage, undersized pipe, or hidden restriction.
Question 6: A bathroom exhaust fan does not relieve humidity, causing persistent moisture problems. The plumber discovers the duct terminates in the attic rather than outdoors. The CORRECT fix is to:
- Add a booster fan inside the duct
- Extend the duct to terminate through the roof or soffit (Correct answer)
- Install a larger exhaust fan
- Add a dehumidifier to the attic
Correct answer: Extend the duct to terminate through the roof or soffit
Exhaust ducts must terminate outside the building; terminating in the attic deposits moisture there, failing to remove it from the bathroom.
Question 7: A copper supply line is found to have pitting corrosion on its interior surface. This type of corrosion is MOST commonly associated with:
- High pH water above 8.5
- Low pH (acidic) water below 6.5 (Correct answer)
- Hard water with high calcium content
- High water velocity above 8 ft/s
Correct answer: Low pH (acidic) water below 6.5
Low pH (acidic) water aggressively attacks copper pipe interiors, causing pitting corrosion that eventually leads to pinhole leaks.
PC Troubleshooting & Diagnostics 3
A sump pump runs continuously but the pit water level keeps rising.
After confirming the pump is running, the NEXT diagnostic step is to: