Installing a pressure-reducing valve with an integral check on the water service turned the building piping into a closed system. To satisfy the code, what must be provided on the water heater side of that system?
- AAn additional hose bibb near the heater to bleed pressure
Bleeding pressure by hand at a hose bibb is not an approved control. The pressure rise happens every heating cycle, day and night, whether anyone is there to open a valve or not.
- BA relief valve with a higher pressure rating
The relief valve rating is matched to the heater and must not be raised. Uprating it removes the last safety device rather than solving the pressure rise that is lifting it.
- CA check valve on the hot water outlet of the heater
A check valve on the hot outlet makes the problem worse by trapping the heated volume even more tightly. It adds another barrier instead of providing relief.
- An approved device or tank to control thermal expansion
Why D is correct
A closed system must be given somewhere for the expanding heated water to go. An approved expansion tank or equivalent device absorbs the volume increase so system pressure stays within the safe range and the relief valve is not used as a pressure regulator.
What this question is testing
Checks that the candidate can recognize when a system has been made closed, understands why heating then raises pressure, and knows that the code demands an engineered control rather than tolerating relief valve discharge.
On the job
This is one of the most common service calls in the trade. A regulator or a new backflow preventer goes in, and within days the water heater relief valve starts weeping onto the pan. Plumbers who do not understand the mechanism replace the relief valve, then replace it again. The real fix is an expansion tank charged to match the static pressure setting, mounted on the cold inlet with support so its weight does not hang on the piping.
Memory technique
Close the system and heated water has nowhere to grow; give it a tank.
Exam tip
Any question that mentions a regulator, check valve or backflow preventer plus a water heater is pointing at thermal expansion.
Where to look it up
IPC Chapter 6, hot water supply and distribution, thermal expansion control. UPC addresses closed system expansion in its water heater chapter instead, so check the code your state adopted.