‘Thermostatic’ means ‘at a constant temperature’. In a shower or any hot water system, an even flow at a constant temperature is just what you want. At one time or another, we’ve all experienced what happens when shower water temperature fluctuates wildly. Someone elsewhere in the house turns on the washing machine or flushes a toilet, and the shower water suddenly goes ice cold or scalding hot – or one after the other.
This won’t happen with thermostatic showers, no matter what’s going on elsewhere in the house. The washing machine could be on, someone could flush the downstairs toilet or turn the bathroom taps on to wash their hands, and still the temperature of your shower will stay steady and comfortable.
In a normal shower, water is drawn from the hot water system and the cold water supply. The shower valves mix the two streams of water by allowing so much cold water, and so much hot water, to flow into the shower head and down onto you, according to the position you set the cold and hot taps (or the temperature control knob) to. If a cold or hot flow is drawn out of the water system elsewhere in the house, the supply of that water drops away, the balance of temperatures in the shower valves changes, and your pleasant shower is interrupted.
Thermostatic shower valves prevent too much cold or hot water from entering the mixing system at any time, so you can enjoy a relaxing shower in peace.