I have a bath which has accumulated limescale inside the piping system; it manifests itself as a very-slow running tap with a weak stream. The tap itself is removable, and I suspect the limescale is inside the pipes just upstream of the taps. What's the best way to clean this out without taking the pipes apart? Vinegar?
If the problem is scale sufficient to seriously reduce flow, you need a major solution and vinegar won't do.
There are acid treatments and reduced lime treatments, both very caustic chemicals that need to be handled by a pro. They are flushed through the whole system to dissolve the lime.
There is an electronic device being advertised that claims to break up the scale and put it back into solution to flush it out of the system. I have no experience with it and heard nothing about it, but it is a major installation.
The solution usually used for badly scaled pipes is replacement. Ferrous pipes seem to build up much faster than non ferrous, but there are problems mixing metals in a system. If you plan a partial replacement, you probably want to consider plastic piping such as PEX.
Most of the solutions offered on various sites focus on reducing buildup by softening water rather than curing the problem after it occurs. The added benefit of softened water is taste and easier rinsing of dishes and clothing.
I don't know if this will work in your situation, but I have a mobile home with very hard well water, and no room for a water softener. The water lines are plastic tubing with some brass shutoff valves. When a toilet or faucet became clogged, I would just turn off and remove the supply line to the fixture and squirt it into a bucket. If that didn't clear it, I would bang on the back of the shutoff valve with a large wrench, and repeat until the line was clear. I would have to do this once a month.
Recently I got smart and installed a small plastic filter from Lowe's between the well and pressure tank. I removed the element, and filled the filter cup full of vinegar. This DID open up two faucets without banging on any valves. As I say, I have plastic water lines. If you have copper, I would make sure you flush them out well immediately after the pipes are clear.