Tub-shower end wall
What's wrong here?
- The shower is controlled by separate hot and cold handles instead of a pressure-balance or thermostatic mixing valve
- The hot handle must be on the right side of the valve
- The tub spout outlet is too close to the tub rim
- Nothing. This installation is compliant
Show the answer and the code reference
The answer
The new tub-shower uses a three-handle valve with separate hot and cold faucets, not the pressure-balance, thermostatic or combination mixing valve that UPC 408.3 requires.
Correct choice: 1. The shower is controlled by separate hot and cold handles instead of a pressure-balance or thermostatic mixing valve
UPC 408.3 requires every shower and tub-shower combination to have an individual control valve of the pressure-balance, thermostatic or combination type that gives scald and thermal-shock protection at the showerhead's rated flow, listed to ASSE 1016/ASME A112.1016/CSA B125.16 or ASME A112.18.1/CSA B125.1. The valve's handle-position stop must be set to deliver no more than 120 deg F, and the water heater thermostat does not count as the control. A three-handle valve is just two faucets and a diverter: when a toilet is flushed and the cold pressure drops, the person in the shower gets hit with full-temperature hot water, which is how small children and older adults get scalded. This valve went in with the remodel, so it is new work and has to meet 408.3.
How to fix it
Replace the valve with a listed pressure-balance or thermostatic tub-shower valve (ASSE 1016/ASME A112.1016/CSA B125.16), and set its handle-position limit stop so the mixed water at the outlet is 120 deg F or less.
Code reference
UPC 2018 408.3 — Individual Shower and Tub-Shower Combination Control Valves
Showers and tub-shower combinations must have individual control valves of the pressure balance, thermostatic, or combination pressure balance/thermostatic mixing type giving scald and thermal shock protection at the rated flow of the installed showerhead, conforming to ASSE 1016/ASME A112.1016/CSA B125.16 or ASME A112.18.1/CSA B125.1. Handle position stops must be adjusted to deliver a maximum mixed water setting of 120 deg F, and the water heater thermostat is not a suitable control for this purpose.
Drills citing 408.3
Minnesota
Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). No Minnesota amendment to UPC 408.3 is known; check ch. 4714 before relying on it. Search excerpts suggest Minn. Rules 4714.0408 amends other parts of UPC 408 (reportedly the shower liner rules in 408.7), not the control valve requirement; that was not confirmed against the rule text.
About the Minnesota Plumbing CodeWhy the other choices are wrong
- The hot handle must be on the right side of the valve. Hot goes on the left as you face the fixture, which is exactly where this valve has it.
- The tub spout outlet is too close to the tub rim. A tub spout has to discharge above the tub's flood-level rim with an air gap (UPC Table 603.3.1 sets 2 in. for an over-rim bath filler, 3 in. where a nearby wall affects it); this one is about 4 in. above the rim, which is normal.
- Nothing. This installation is compliant. A three-handle compression valve mixes with two independent faucets and cannot hold the outlet temperature when the cold pressure drops, so it does not meet UPC 408.3 for a new or replaced shower valve.