hi i have just purchased a external pipping complete shower set unit. The mixer's body and pipe fitting is external so it visible, its not a flick mixer it has separate hot and cold water quarter turn spindles and the just above the body it has a diverter with diverts in to a hand held shower. After the product is fitted i found the water flow is not consistent and unstable, when i turn it on the water switches to hot then cold repeatedly. After contacting the manufacture, their reply was it is my plumbings problem but other existing showers in my house works perfectly fine except this one. Can some on please help me out. Many thanks.