"I bought this, as I was advised my plastic plumbing should not be exposed to the very hot water from my boiler/tank. The boiler can't be turned down due to the risk of storing water at a temp that Legionnaire's disease likes! This valve mixes hot & cold and reduces the temp to about 50C as it passes from the tank. This is safer for everyone and the pipework. I know someone who didn't fit one and has had hundreds of pounds of repairs after pipe failure. So a good buy."