Journeyman Plumber ExamWater Supply SystemsHard
A plumber is troubleshooting a domestic hot water recirculation system in a large residential building. The system uses a dedicated return line and a recirculation pump. Residents on upper floors are complaining about long wait times for hot water, despite the pump running continuously. What is the most likely cause of this issue?
- AThe recirculation pump is undersized for the system's demand.
- BThe hot water supply line to the upper floors is undersized.
- CThe check valve on the recirculation return line is installed backward.
- DThe water heater's thermostat setting is too low.
Show answer & explanationAnswer & explanation
Correct answer: C. The check valve on the recirculation return line is installed backward.
If the check valve on the recirculation return line is installed backward, it will prevent water from flowing back to the water heater through the return line. This effectively stops the recirculation loop, meaning hot water is not continuously circulated, leading to long wait times, even if the pump is running. The pump would be working against a closed valve.
Why the other options are wrong
- A. An undersized pump would lead to slow but still present hot water, not typically a complete lack of circulation that causes long wait times.
- B. An undersized supply line would reduce flow rates, but hot water would still arrive in a reasonable time if the recirculation system is functioning correctly.
- D. A low thermostat setting would result in lukewarm or cold water, but not necessarily long wait times if the water is circulating.
Recirculation System Check Valve
A check valve in a hot water recirculation system ensures that water flows in only one direction through the return line, preventing cold water from entering the hot water supply or the pump from short-cycling.
- Essential for maintaining proper flow direction in a recirculation loop.
- Incorrect installation (backward) will completely stop recirculation.
- Typically located on the return line, before the pump or water heater connection.
Memory trick: Backward Check valve Blocks Circulation, Causing Cold.