After some work on my water heater, my Grohe thermostatic shower valve only has low flow. I will end up taking it apart to check the filter screens, but at first, I had good cold volume, but now both hot and cold are quite slow, so I think it's more likely to be pressure balance function. The WH was changed and it had shutoff/isolation valves, so cold wasn't really affected. I think it's more likely that the pressure balance spool is stuck (I'm assuming it has one in addition to the temperature control). This part is the volume/diverter control 47-364 and 47-302 is the thermostatic control. Does anyone know whether it's more likely in one verses the other? I don't want to take things apart without a little more info.