When I turn the water on nothing comes out of the shower head and all other fixtures work fine. Could this be a clog in the pipes?

The boiler is clogged or has a hole in it.

If the toilet is the only fixture in the bathroom group that is having an issue, then there is a partial blockage in Strap of toilet or in drain pipe close to toilet. If other fixtures are showing sluggish drainage, then the main drainage line is clogged. If all is fine with tub lav shower etc., pull toilet from floor and carefully turn upside down, and look to see if anything is visable. if so remove it and reinstall with new seal(wax ring). Also, look into pipe and see if any water is standing in it. If water is standing in pipe, the drain line is clogged and must be rodded(snaked) out to cure problem

Moen products are the worst on the market. Remove the trim. Check that both stop valves are fully open. Then get both cartridges and replace them. Moen will warranty them, but you have to wait for delivery.

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.

To clarify your question, are saying that you just had a new water heater installed in your house and the shower head in the bathroom can't get water through it? If that's what you meant, the water restrictor in the shower head is plugged with sediment. This often happens during water main shut offs and then turned back on. It shocks the sediment on the inside pipe walls. The first places it affects are shower heads and faucet aerators. Remove the shower head and clear the clog or replace with a new shower head. If this is not what you meant to say, then rewrite your problem.

for starters check fo rotten washers get rid of black pieces take shower head some where to blow high presure air thru head good luck

You need to replace the tub diverter/spout. There are two kinds, I hope you have the kind with
an allen head set screw on the bottom side of the spout near the shower wall. These are super
easy to replace ! Loosen the set screw, twist the spout a little and it should slide off. When installing
the new spout, smear some vaseline on the copper pipe sticking out, this will help seal the new O rings in the spout.

The other kind of spout has pipe threads in it. They can be a little more tricky. I got called to a
house one time. The plastic female threads on the spout cracked when the plumber installed it.
The water ran down the inside of the wall and did damage down stairs. The leak could not be seen
until the sheet rock down stairs fell down from being soaked. You need to put some pipe dope on the threads, then tighten the spout on by hand, so as not to scratch it with a pump pliers.

I hope this helps !

Every faucet and shower have a water saving restricter in them. Remove them from the shower head and end of the faucets.
They are about the size of a dime and with about 1/8" hole in them in which water flows out. So the flow is getting restricted from 1/2' flow to this giving you a water saving about a 1.5 gpm.

Below is some more information for the web site please check it out for further help.
http://www.inspectapedia.com/water/Poor-Water-Pressure-Diagnosis.htm
Poor water pressure just at certain plumbing fixtures? poor cold water pressure, hot water pressure, or both hot and cold water pressure or flow that is observed just at some plumbing fixtures in a building while flow and quantity are good at others suggests that the water flow or pressure problems are local to certain runs of supply piping or to the specific fixtures. Check the following first:

1. Clogged aerator or strainer on sink faucets - clogging by dirt, debris, corrosion, can significantly reduce both hot and cold water flow at a sink where the strainer needs cleaning or replacement. Unscrew the strainer from the faucet and turn on the water - if the fixture pressure or flow is much better you've probably found the problem.
   
   Look at the aerator/strainer: inspect it, clean it, perhaps soaking it overnight in vinegar to remove corrosion and mineral build-up, or just install a new aerator/strainer.

sounds like there may be some blockage in pipes. try to run a long snake through both drains or run all fixtures in bathroom and try plunging vigorously in tub and shower while running water. if nothing still, it may be possible that your underground plumbing is back graded or incorrect fittings and plumbing installation.

Sounds like your outlet at the top has clogged with grit/dirt. Turn the shower off, remover the entire shower head hose from its base (where it screws into the wall or pipe. Turn water back on. If you get a steady flow (as you should) the problem is isolated to the shower head/hose. Detach the shower head from the hose and clean the screen inside, attach hose back on first, try water again, if this flows then your blockage is in the head itself. After removing and cleaning the screen inside the shower head, reattach and run water, this should fix your problem, if not, you may need a new shower head. If the water will not flow to the outlet pipe alone, either your shower switch is broken or you have a serious plumbing problem.