Why Low Water Pressure in Just One Fixture?

[wenrat]

I live in a 2-storey house that is 25 years old. Most of the plumbing fixtures are also 25 years old.

A few days ago the water pressure in the main upstairs tub and shower became very weak. It was still fine elsewhere, including the two sinks in the same bathroom.

I removed the tub spout to investigate, and the water pressure coming from the pipe was weak. What is the problem and how do I fix it?

Yesterday the pressure in a sink in a different bathroom just about disappeared. Is this problem related to the previous one?

 

[Markts30]

What type of piping does it have?
Copper or galvanized?
anyting changed recently?

 

[Sponsor]

 

[Plumber1]

Take the diverter out and see if you see a possible problem.