You are making up a combination relief valve on a new 50-gallon tank. Where does the code require the temperature-sensing element of that valve to end up once the valve is installed?
- Within the top 6 inches of the tank, in contact with the hottest water in the vessel.
- BInside the cold water dip tube, so that incoming water passes across the element.
The dip tube carries incoming cold water. An element there would read cold while the top of the tank boils.
- CIn the discharge piping just downstream of the valve body, so the element stays dry until relief occurs.
An element in the discharge line senses nothing until water is already flowing past it, which is far too late.
- DAt the midpoint of the tank shell, where the average stored temperature can be sensed.
Mid-tank readings lag the hottest layer, so the valve would open only after the top of the vessel is already dangerously hot.
Why A is correct
A runaway water heater overheats from the top down, so a valve that senses the top 6 inches of stored water sees the hazard first. That is why the code fixes the element location rather than leaving it to the installer.
What this question is testing
Whether the candidate knows the installed geometry that makes a T and P valve work, not just that one is required.
On the job
Field crews sometimes install a pressure-only relief valve on a side tapping, or extend a T and P valve out on a long nipple so the probe never reaches the water. Both defeat the temperature function entirely. When you replace a relief valve, check the probe length against the tapping so the element ends up in the water, and never plug a factory T and P tapping to move the valve somewhere more convenient.
Memory technique
Heat floats, so the probe sits in the attic of the tank.
Exam tip
The T and P element belongs in the top of the tank; anything that keeps it out of the hottest water is wrong.
Where to look it up
IPC Section 504 covers water heater safety devices, including relief valve requirements and installation. UPC states similar requirements in its water heater chapter under different section numbers.