Hand held shower leaking

[Monaco]

I have a mixer shower which consists of a main overhead shower head and a second hosepipe style shower head (see photo).

When I turn the shower on, the water comes out of both heads at the same time.

This only started happening about a year after it was all installed. It’s about 3 years old now and progressively getting worse.

Twisting the little valve doesn’t do anything (it used to, just not anymore since the problem started):

Which part do I need to replace?

 

[blup]

The diverter valve is rusty or worn inside the body of the shower mixer. You may be able to get a replacement. The shower doctor has a helpful service in this respect. Just specify the make and model or send a photo.