I apologize if this is well covered territory, however, my exhausted search on the internet has not yielded any actual solutions that have worked. Maybe my Google-Fu is not black belt worthy...
Additional disclaimer: I am a decent DIYer, though perhaps not in tune with all of the terms related to plumbing.
I have a relatively new house (3 years old); good water pressure entering from city water at the street, tankless water heater, and good pressure at exterior spigots, all faucets, the washer and dishwasher. The house has four showers (one on the first floor, three on the second floor); the only one with really decent water pressure is the master bathroom (second floor), which has two shower heads. Even when both of those shower heads are on, there is pretty good pressure.
The other three showers, however, have poor water pressure. We never really used the other showers because our kids are really little and have always taken baths or have been showering in the Master bath. Well, now we are moving them to their bathrooms and its a bit undoable with the poor pressure.
All of the fixtures are Mirabelle (Key West), single handle. I took one of them apart to see if it was the hot/cold mixture (mixture was good), or if it were the control valve that has set screws on both the hot side and the cold side that you can tighten for less pressure, and loosen for more pressure. It had about half a turn left to be full open, which I turned it to, yet the volume was essentially unchanged.
Someone told me that the pipes may be different in the Master bathroom? but that doesn't really make sense to me, as the pressure should still be the same when it comes out of the shower head...
Im really stuck - any advice would be greatly appreciated!