Grohe shower drip -- please help!!!

I have a Grohetemp 3/4 inch mixer and 3 Grohe 3/4 volume controls (1 each for the body sprayers, fixed shower head and handheld). The shower drips constantly (mostly from the body sprayers, but the others drip a little too). I have replaced the cartridges in the volume controls because the plumbers I've spoken to all insist that this is the problem. Of course, the shower still drips like crazy. Here are my product numbers:

Mixer: 34 902 -- http://www.grohecatalog.com/product/34902
Volume controls: 29 268 -- http://www.grohecatalog.com/product/29268/

I've spent tons of money on plumbers who can't seem to fix my drippy fixtures... any help would be greatly appreciated! Thanks!

Have you called Grohe?

Absolutely! I've called Grohe several times... they too said that it was probably the volume control cartridges, and they even sent me new cartridges for free. But like I said, the problem is not the volume control cartridges.

How long do they drip? Unlike a tub with a shower valve, when you turn off a shower, there is no place for the water to go like it does in a tub...where if falls down and out the spout. The showerhead and arm will hold some water and drip for awhile, maybe hours before it empties enough to completely stop.

Unfortunately, the fixtures drip forever. In fact, we ran a test: we have a cut-off in the utility room... I turned off the water to the shower entirely, opened all the valves and let the fixtures completely drain... after everything was bone dry, I turned the water back on in the utility room and the body sprayers begin dripping again (even though we never opened the valve to turn them on).

All of the plumbers we've spoken to insist it's the cartridges in the volume control, but that clearly isn't the culprit. I'm just getting tired of paying plumbers to make an incorrect diagnosis!

Thanks again for your help.

The volume controls are the only possible problem.

You see, the thermostatic mixer is live all the time, only its outlet is controlled.

The outlet is controlled by what? The volume control.

You most likely have a problem with the seat, which sits further inside the valve body. (Look at #7 on the parts explosion)

Problem solved

You were correct... the problems were in the seats. The cartridges were working fine. In fact, a bunch of teflon tape around the threads in the seat did the trick.

Thanks.