Shower question

[BobbyJoe]

Hi I have a thermostatic rainfall shower and it also also has a hand held shower with hose attached to it. I was checking the temperatures by adjusting the thermostatic bar valve and when the bar valve is set at 40c the rainfall shower is around 37 degrees but the hand held shower is 40c, so their is a drop of around 3 degrees in temperature.

My question out of interest is why is their a slight difference between the two and do all thermostatic showers do this?

Thank you for any advice

 

[Ric2013]

My guess would be that the water may be losing 3°C in the process of warming up the metal in the length of pipework to the rainfall head, so this might happen only for the first few minutes. Since the termostat is on the mixer and not on the outlet, it has no way of 'knowing' the water is coming out 3° colder. If not that, then I have no idea either, I'm afraid.