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We had some work done on the mains cold water feed into the house. At first everything worked just fine but after about a day when the top floor shower is now switched on there's a rapid banging noise and reduced hot water flow. Switching the cold water on, just a bit, in the basin next to the shower stops the banging but the hot water flow doesn't increase. The hot water flow from the tap in the basin (and every other tap in the house) is excellent.

What would cause this? Is it trapped air? Is the pressure too high for the shower?

Update: It turns out that a little piece of plastic had worked it's way up to the shower and got trapped in the hot/cold water mixer. Took a plumber about 1 minute to pop the cap off, clear out the mixer and put it all back together. Sorted!

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This Question might be helpful. – Tester101 Oct 19 '12 at 12:37
up vote 4 down vote accepted

Sounds like there's gunk stuck in the shower line somewhere between the branch for the shower and the shower's hot water valve. HOPEFULLY it's stuck right there at the valve.

One thing you can do is shut off the hot water in the house, then remove the knob and valve stem for the hot water in the shower, then turn the water back on. Water will flow out of the valve (I'm assuming the valve is in a water proof area like the shower itself) - and hopefully this will flush the gunk out of the line, restoring the water flow.

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Thanks, I'll try taking it apart and see if I can see anything. – snowdude Oct 19 '12 at 13:00
You may also have gunk stuck in the shower head itself. Those are usually easy to take off and clean out. – Wayfaring Stranger Oct 19 '12 at 18:39
I thought about that but that would affect the cold water flow in the shower as well. – The Evil Greebo Oct 19 '12 at 19:09
It's not the shower head. I took the head off the hose and it still had the same problem, the water stutters out as if fired from a machine gun. I tried disconnecting the whole unit but the screws need a little more force than I am comfortable using so I think I'll leave it to a plumber. – snowdude Oct 20 '12 at 10:01
Can you post a picture of your fixtures, and we can direct you on how to remove it properly w/o too much force. – The Evil Greebo Oct 20 '12 at 12:42

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