Journeyman Plumber ExamWater Supply SystemsHard
A plumber is troubleshooting a domestic hot water recirculation system. The homeowner reports that hot water is no longer 'instant' at distant fixtures, and the recirculation pump seems to be running constantly. Upon inspection, the plumber finds that the check valve in the recirculation line is stuck in the open position. What is the most direct consequence of this check valve failure?
- AThe recirculation pump will experience increased wear and tear due to cavitation.
- BThe system pressure will increase significantly, potentially damaging fixtures.
- CCold water will backflow into the hot water supply line, mixing with hot water.
- DThe water heater will continuously cycle on and off more frequently.
Show answer & explanationAnswer & explanation
Correct answer: C. Cold water will backflow into the hot water supply line, mixing with hot water.
If the check valve in a hot water recirculation line is stuck open, it allows cold water from the cold water supply or from fixtures to flow backward into the hot water recirculation loop and mix with the hot water, significantly reducing the temperature of the water delivered to fixtures.
Why the other options are wrong
- A. Cavitation is typically caused by low pressure on the suction side of the pump, not directly by a stuck-open check valve allowing backflow.
- B. A stuck-open check valve would not cause a significant increase in system pressure; rather, it would lead to temperature issues and potentially increased pump run time.
- D. While the water heater might run more due to constant circulation of cooler water, the direct consequence of the stuck-open check valve is the backflow of cold water, not necessarily just more frequent cycling.
Recirculation Check Valve Failure
Malfunction of the check valve in a hot water recirculation system, typically allowing cold water to enter and mix with the hot water in the loop.
- Check valve prevents reverse flow
- Stuck open allows cold water into hot line
- Results in lukewarm 'hot' water
- Causes recirculation pump to run longer
Memory trick: Stuck valve, cold flow, instant hot water is a no-show!