Facilities layer the protection. The plumbing code requires shower valves that are balanced-pressure, thermostatic or both, with a 120 degree F maximum stop, and bathtub valves supplied through an ASSE 1070 temperature-limiting device. Arizona's assisted living rule also holds resident-area hot water to 120 F. Valves wear out, so testing and records matter.
What does the plumbing code require at showers and tubs?
The 2024 International Plumbing Code (IPC) sets rules by fixture. For an individual shower or a tub-shower combination, Section 412.3 requires valves that are "balanced-pressure, thermostatic or combination balanced-pressure/thermostatic valves that conform to the requirements of ASSE 1016/ASME A112.1016/CSA B125.16." They have to be "installed at the point of use," and must be "equipped with a means to limit the maximum setting of the valve to 120°F (49°C), which shall be field adjusted in accordance with the manufacturer's instructions." It also says "In-line thermostatic valves shall not be utilized for compliance with this section."
Bathtubs and whirlpool tubs get a separate rule. Section 412.5 says they "shall have or be supplied by a water-temperature-limiting device that conforms to ASSE 1070/ASME A112.1070/CSA B125.70" or by a water heater complying with ASSE 1082 or 1084, with a maximum setting of 120°F, "except where such valves are combination tub/shower valves in accordance with Section 412.3."
Gang showers, where several heads share one tempered supply, are different again. Section 412.4 requires the supply to be controlled by an ASSE 1069 or CSA B125.3 automatic temperature control mixing valve, or each head to be individually controlled by a point-of-use valve of the 412.3 type.
Phoenix adopted the 2024 IPC with amendments under Ordinance G-7397. Its amendment list covers other sections, such as 403.2, 410.2, 424.2 and 604.4, but not 412.3, 412.4 or 412.5. Other Valley cities adopt their own editions, so confirm the edition where the building is.
What do the ASSE standards actually do?
Each standard covers a different job, which is why a facility usually needs more than one. From ASSE's own descriptions:
| Standard | What it covers |
|---|---|
| ASSE 1016 | Automatic compensating valves "intended to be installed at the point of use" for showers and tub-shower combinations |
| ASSE 1017 | Temperature actuated mixing valves "installed at the hot water source," not meant for point-of-use temperature limiting |
| ASSE 1069 | Automatic temperature control mixing valves meant to "reduce the risk of scalding and thermal shock," for gang showers and similar |
| ASSE 1070 | Water temperature limiting devices for sinks, bidets, lavatories and bathtubs "to reduce the risk of scalding," which "are not designed to address thermal shock" |
Thermal shock is a sudden change in water temperature at the outlet. ASSE describes the 1016 valve as an automatic compensating valve that controls the water temperature at a shower, while the 1070 limiter is built to cap the maximum and is not designed to address thermal shock. That difference is why the code asks for different devices at different fixtures.
Why isn't a limit at the water heater enough?
A source-level valve protects the whole system but not the last few feet. ASSE 1017 valves are, in its words, "installed at the hot water source." If the one at the heater fails, or if a fixture's own valve wears out, residents can still get a bad temperature at one tap. A point-of-use valve limits what that one fixture can deliver.
The reverse also holds. A manufacturer's manual for one pressure-balancing shower valve warns that it "may not protect the user from scalding when there is a failure of other temperature controlling devices elsewhere in the plumbing system." Each layer covers for the others, and none replaces them.
The 120 degree stop is also a field adjustment, not a factory promise. The same Symmons manual says "failure to adjust the limit stop screw properly may result in serious scalding." The IPC requires the setting to be "field adjusted in accordance with the manufacturer's instructions." Someone has to set it, and someone has to check it again after any valve is replaced.
What does Arizona's assisted living rule add?
The licensing rule sets the target the plumbing is meant to hit. Under A.A.C. R9-10-819(A)(6), a manager shall ensure that "Hot water temperatures are maintained between 95º F and 120º F in areas of an assisted living facility used by residents." The detail of that rule, including why it has a floor as well as a ceiling, is in our page on the hot water temperature required in Arizona assisted living.
The Consumer Product Safety Commission gives the scald logic in numbers. Most adults "will suffer third-degree burns if exposed to 150 degree water for two seconds," with burns also from a "six-second exposure to 140 degree water or with a thirty second exposure to 130 degree water." The CPSC also says "The majority of injuries and deaths involving tap water scalds are to the elderly and children under the age of five." Anyone slower to step away from hot water has less margin than those exposure times suggest, which is the case for the 120 degree cap and for valves that are tested.
How should a facility test and document the protection?
Treat temperature limiting as maintained equipment. This is practical advice built from the rules above, not a mandated schedule.
- Record the setting of each limit stop or limiter when installed, and re-check after any valve cartridge, shower valve or faucet is replaced.
- Measure the delivered temperature at resident outlets, not just at the heater. Our page on why commercial water heaters run short of hot water explains the supply side.
- Investigate any room where residents report sudden hot or cold swings, since a worn cartridge is a common reason for that complaint.
- Keep the replacement history by room, so repeat failures stand out.
- Keep temperature limiting in view when the building runs a hot water loop for Legionella control. See the Legionella water management plan page for how storage and delivery temperatures fit together.
A licensed plumber should do valve replacement and field adjustment, because the 120 degree setting depends on the manufacturer's instructions for that exact valve.