We have a shower in our house that we've never used (have always used the tub). Now we're trying to use the shower but can't get water to come out of the shower head. There is a valve on the side of the shower head that turns but nothing happens. I just don't know how to make it work!

Overflow? Seal around drain may be good enough for shower, but leaks with a little more pressure from the filled tub. Filled tub may flex the tub and drain components. What about the overflow. I bet some water is going over, but it isn't used for showers. Double check. Paper towels tied in stratigic locations always help me find a leak. Leak makes the towel soak up water nearby. It's most wet at the point of leak.

When you turn off faucets other than your tub or shower you will note that the water stops fairly abruptly. Not so with a shower head or tub spout. Some water always dribbles out even after you have turned it off. This small amount of water then evaporates leaving behind the iron that was dissolved in your water. This also happens if any faucet has a slow drip. There are products that will easily remove the rust stains. CLR, Iron Out, or Iron Ike are all good products that will remove the stain. Available at hardware stores, plumbing supply houses, and, ugh, Home Depot or Lowes. Please support your local business owners by purchasing there.

Make sure the hot water is turned back on. Pressure balancing valves won't work if both cold and hot water is not on. Pull shower head off and test to see how it flows out of the shower arm. If good, clear out shower head. Whenever water is turned off for a time, and then turned back on, restricting shower heads and aerators usually get clogged. In the future, always open up a tub spout before turning water back on. This releases the air and other debris most effectively before testing other fixtures in the house.

there are two kinds of cloudy. white cloudy indicates you need to use a Clarifier in the water to get the small particulates out of the water each week. Brown cloudy water indicates you are getting into the hot tub before you shower or bath and get nice and clean before getting into the hot tub. Hot Tubs are therapy vessels and those who get in should be showered and clean before using it or the water will always go a brown cloudy and you will use more chemicals than needed to maintain the cleanliness of the water.

You will have water coming out of the shower head when you have really good water pressure. There might be more water volume coming out through the valve then what the tub spout can handle and in turn sends the water up to your shower head. When you fill your tub try turning the water only half way on not at full pressure, does this keep the water from coming out of the shower head? Most likely your valve has a 3/4" supply line while your shower head and tub have only a 1/2" supply line. Sounds like you have more volume to the valve than what the tub spout can handle. You might consider one of two things: 1) you can put a water regulator on the main supply line going into the house to lower your pressure, or 2) change out the supply line to the tub spout, increasing it from 1/2" to 3/4". Let me know whats going on.

if the pipe feeding the tub spout is pex, cpvc or poly then it needs to be replaced with a pipe with a larger i.d. like copper or galvanized or reduce the pressure to the house.

these valves can be adjusted by removing the handle and adjusting the white gear that regulates the hot and cold that come out, try going more to one way if it gets colder then go the other way.

The only possible explaination is that the water is finding it easier to go up than down. Water is lazy, just like me. ;)

Use an allen key to remove the tub spout. It's underneath and awkward. Once the allen key is loose, the spout just slides off. Try running the water. This may solve your problem and all you'll need is a new tub spout. If not.....

Turn the water off to the house.

Use an allen key to remove the handle.

Use a phillips to remove the trim plate (2 screws). Cut the silicone around the trim if it's there (which, in a proper installation it shouldn't be, but...)

Unscrew the nut (usually chrome) holding the cartridge into the brass body of the valve. The cartridge pulls straight out. Check for restriction in the ports of the cartridge itself. Check for restriction in the line going down to the tub spout. If you can't find anything, replace the cartridge.

Reassemble & Enjoy!

i am assuming you have hot water in same bathroom and that its fed by the same pipe? if so ask yourself did i have anything done recently that may have affected the shower ?if not i would think you have some kind of a blockage in fitting. one way to try to clear it is shut off water to house open shower fitting to what used to be the hot side when working,leave shower open,go o lowest level of house open hot side in sink you may get lucky and vacumn(think ****)debri from shower good luck .

Does the tub spout water flow stop when the shower knob is pulled?

Was the systems pipping flushed before the shower head was installed?

It may be clogged, remove the shower head and then attempt to operate. If it is clogged you will see debris trapped in the screen at its connection point. The shower head can be disassembled - cleaned - reassembled

Is the shower head an adjustable type, that may be in the off position?

Good luck
Aduz