I have a shower that has very low flow from the hot and cold water and also from the shower when you turn the valve to switch it to the shower. All of the other fixtures in the house have strong flow including the sink in the same bathroom. Unfortunately there isn't an easy way to get access behind the shower (tile on both sides of the wall). Does this sound like something that could be caused by bad cartridges? What about some kind of corrosion built up in the pipes? How can I go about diagnosing this without ripping open the walls?

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    Has the flow always been low, or has it gotten worse over time? Where are you from? Some places have water saving plans in place, so there could be pressure reducing devices in place (that cannot be removed). – Tester101 Jan 6 '12 at 19:31
  • It is a spare bath so doesn't get much use. It has been slow at least for the last 10 years. The fixture is probably 30 years old (same age as the other bath that isn't slow) so I wouldn't expect a water saving device to be to blame. – Doug Porter Jan 6 '12 at 21:14
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    What kind of fixture is it? Many fixtures have components that are serviceable from in front, after removing a handle and faceplate. If that applies to you, you might try taking out the valve cartridge and soaking it in vinegar to dissolve any mineral build-up. – Shimon Rura Jan 9 '12 at 3:12
  • Do you have hard water (lots of minerals in the water)? Over time, the minerals can build and block pipes and valves, especially hot water pipes. – Pigrew Sep 27 '12 at 1:52

If you have a shutoff valve feeding that bath or that shower, I would check:

  1. Is it on all the way?
  2. If it is, you can sometimes disassemble it in place (of course turn the house water off first). The typical valves for this application are gate valves, which can get a lot of gunk in them. Disassembly will also let you see if the problem is before or after the valve (with valve disassembled, turn on house water for a second; Did you get good flow or not?).
  3. If you disassemble a gate valve don't be surprised if you need a new stem seal (the seal that keeps it from leaking around the shaft).

Sometimes there is a screen in the shower head that can collect mineral deposits over time. They look kind of like white beads. Try removing the shower head and see if any more water comes out.

  • Or just replace the entire shower head. They are quite cheap and sometimes it's more than the mesh that clogs. Alternatively soak the entire shower head in a bucket with 20% CLR. – Warren P Jan 7 '12 at 19:37
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    I am careful replacing shower heads, because some of the new ones have severe water saver washers that are hard or impossible to remove, and I end up with a dribbly shower. (I live where there is plenty of fresh water.) – xpda Jan 9 '12 at 1:09

Remove the shower head, then try the shower. If you get full flow, replace the shower head. If you get low flow, probably there is a buildup of corrosion inside the pipes. We have replaced pipes recently and the amount of crud that can build up is unbelievable (sorry I did not take photos).

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    The faucet in the tub does the same thing. Do you think the shower portion could be affecting the faucet part as well? – Doug Porter Jan 8 '12 at 19:03
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    @Dougman: if you have a single set of faucet valves with a diverter, you could get lucky and be suffering from buildup in the valves. But the buildup is probably in the pipes. I'd start hunting for some kind of hidden plumbing access, possibly from the hall outside the bathroom, because you're going to have to replace something inaccessible. – Norman Ramsey Jan 10 '12 at 17:49

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