Hello, I have run into a problem that I can't solve and maybe someone out there can help. This is a new building. I have a single lever shower valve with diverter (MIC). Cartridge is pressure balance rotary style. The pressure in the valve fluctuates i.e. when I initially turn the valve on the pressure is great. I shut if off an turn it on again and the pressure drops in half. If I turn it off again and on again the pressure will still be low however, if I wait a few minutes then turn it on the pressure will be normal again. I have pulled check stop valves and poppets and they appear to be functioning properly. I have replaced the cartridge but that didn't help. I have pulled the cartridge and augered the hot and cold input channels in the valve looking for blockage but they are clear. Pressure in all other areas in the apartment is normal. The pressure balance valve on the cartridge is working properly. Any ideas? Thanks in advance.

I would suggest flushing out the pipes to your shower valve. Sometimes bits of sediment can sit in the elbows of pipes & get shoved around with the on/off movement of water. You'll need to shut the water off to the shower, remove the cartridge & everything else that would blow out when the water is turned on (i.e. seals), stick a piece of plastic under the valve body to keep water from flowing back into the wall & plug your drain. Turn the water on & off to jerk the flow around & hopefully you'll push whatever sediment out of the pipes.