The water pressure in my master bath is significantly lower than the bathroom directly next to it. The master bath is the only area with water pressure issues. It has been like this for over a year now with no signs of leak. The hot and cold water is effected. I have a 3 valve set up and when I turn the bath faucet on for a minute then turn the shower faucet on it seems to increase the pressure for a short period. I am at a loss.

Remove shower head, run water w/o shower head for few minutes... Clean shower head.. If there is a Flow Restrictor inside the shower head mount / thread - you can remove it, if you wish... Reinstall shower head... see if that helped... Back to you... Milo

Remove shower head, run water w/o shower head for few minutes... Clean shower head.. If there is a Flow Restrictor inside the shower head mount / thread - you can remove it, if you wish... Reinstall shower head... see if that helped... Back to you... Milo

I removed the shower head and found that the water pressure for hot and cold water is still extremely low even after running the water for a few minutes.

3 valve set up

Remove and inspect diverter valve.

Remove diverter valve, turn on water briefly to blow out any debris. Inspect diverter valve, repair or replace if necessary.

Shower head flow restrictor cleaning was the first and easiest step to do. Now, do what Harold suggested. Also, your faucet may have "stops" ( valves that close h/c water ) built into the body of the faucet itself. If you have the stops, make sure they are fully open. Back to you. Milo