Why anti-scald valves exist
In an older shower with a plain mixing valve, flushing a toilet or starting the washer drops the cold-water pressure, and the shower suddenly runs hotter. Anti-scald valves are built to react to that change so the person in the shower isn't burned or shocked by cold.
Modern plumbing codes generally expect showers to have this kind of protection when a valve is installed or replaced. Exactly what applies to your bathroom is a question for the plumber and, where a permit is involved, the city.
How they compare
| Pressure-balancing | Thermostatic | |
|---|---|---|
| What it senses | The pressure of hot versus cold | The actual temperature of the mixed water |
| Handle setup | Usually one handle for on, off and temperature | Often separate controls for temperature and volume |
| Flow control | Volume and temperature tied together | You can turn the flow down without changing temperature |
| Moving parts | A spool or diaphragm inside the cartridge | A thermostatic element in the cartridge |
| Hard-water sensitivity | Scale can make the spool stick | Scale can slow the thermostatic element |
| Where it's common | Most standard tub-showers | Higher-end showers and multi-outlet setups |
Which one fits
- IfYou are replacing a valve in a standard tub-shower and want a simple, common partThenA pressure-balancing valve is the usual choice.
- IfYou want to set a temperature once and adjust flow separatelyThenA thermostatic valve does that.
- IfThe shower will feed a handheld, body sprays or more than one headThenAsk about thermostatic valves and diverters sized for it.
- IfYour current valve has an anti-scald cartridge that just dripsThenA cartridge replacement may be enough; no new valve needed.
Terms you will hear
- Rough-in valve
- The valve body that sits inside the wall and connects to the pipes.
- Trim
- The visible handle, plate and escutcheon that cover the valve.
- Limit stop
- An adjustable stop that sets the hottest position the handle can reach.
- Diverter
- The part that sends water to the spout, head or another outlet.
- Stops
- Small shutoffs on the valve that isolate the shower from the rest of the house.
What to ask
- Does my current valve already have anti-scald protection?
- Can my problem be fixed with a cartridge, or does it need a new valve?
- Will the new valve fit behind my existing tile opening?
- Will you set and show me the limit stop?
Common questions
Is a thermostatic valve always better?
Not always. It gives finer control, but for a standard tub-shower a pressure-balancing valve does the job and parts are common.
Can I add anti-scald protection without opening the wall?
Only if your existing valve accepts an anti-scald cartridge. Otherwise the valve body has to be replaced.
Why does my anti-scald shower never get hot enough?
The limit stop may be set low, or scale may be stopping the cartridge from moving fully. Both can be checked through the trim.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.