Low water pressure at the first floor?

Q: We have a 2-story house in Sammamish. The water pressure in the kitchen and bath room at the first floor appears to be low (it’s been low since we moved in). Warm water is worse than cold water. However both cold and warm water at the second floor seem to be just fine. I’m wondering if others have seen similar issue before. What would the normal reason be for this issue? Who do you start the diagnosis with, local water company or a plumber? Do you have a plumber recommendation?

A: Do other areas of the first floor have the same issue? Like an outdoor faucet?

Q: Both of the 2 outdoor faucets on the first floor level, one at the front and one at the back yard, appear to be fine.

A: I would do some of my own investigation first before calling plumbers, which are expensive.

Buy a book on plumbing in the house (Lowe’s or Home depot should have), read it to understand how the pipes go around the house, go to garage (heater) to check hot water pipes, go down to crawl space to check first floor pipes.

A: Then it seems you are clogged at a Tee somewhere, most likely. Is the plumbing accessible in the crawlspace?

Also, have you verified that if you remove the shower head you still have bad pressure? It could be possible you have water restricting heads, but unlikely.