I have an old house - galvanized pipes. I was rinsing the bath/shower when suddenly, there was a huge loss in water pressure. Hot, a trickle out of tub spout and shower - Cold, same as hot, a trickle. Called plumber - he replaced valves behind the hot & cold faucet handles. Still no pressure. He thinks there is blockage in between and the only way to fix it, is to go into the wall to replace the "valve" in between?!? Is this true or is there another way to clear out the blockage? From diagrams I have looked at, it seems as if there should be a tool or something to bend around into the pipes to clear it out. Or blow some air through it? Maybe there are stops of some sort in there that I don't know about?!? I don't want to make it worse by poking and prodding a wire hanger in there...

Any help would be greatly appreciated before he tears up stuff...