Water just trickles out

Hello Mark
is the water still coming out the bottom when you pull up the lever to make the shower come on ? if it is then the tub valve is bad . if little or no water come out of the bottom then the head is going to be clogged and you have have buildup inside the filter /screen which could be located in the end of the hose at the head or inside the head unit itself. .

this is caused by hard water buildup, foreign matter or a defective/damaged "cartridge". it is easily repaired even for a novice and you can view the installation instructions here: http://www.faucetdirect.com/mediabase/specifications/delta_t13020_inst_1027.pdf
unfortunately the cartridge costs almost as much as the whole diverter kit so do what i do...buy a new one and put the old one (as long as it is not clearly visibly damaged) in a jar of CLR (any calcium lime removing product will do) for a couple of hours and then rinse it out/off. then you just swap em out every time it drips. hope this helps but if you need anything else just ask:)

check the placement of the valve,, it may be 180 degrees out,, also,, try it with the shower head off, it may be clogged

The cartridge should have pins that create proper alignment with the supply lines. New single handle faucets have limiters that allow you to control the amount of hot water. Check the limiter position. Its also possible that the cartridge is clogged with debris. Modern low flow plumbing appliances reduce flow by reducing the water passages inside the unit. Therefore they are more easily clogged.

Replace valve canister- no construction- just remove after taking time to shut off water- a few screws and the job takes 15 minutes. I take for granted you have good water hot/cold to the fixture. This fix will cure most temperature balance problems.
The single lever system is a EZ care system. Note the canister can malfunction faster when exposed to untreated hard water.

Hidden under the lever is a little hex screw. Use an appropriate hex a.k.a. "Allen" wrench to remove the handle. You might want to shut down the water service first to save your shower until later.

It sounds like it has mineral deposits in the hot water side. Try taking the internal valve parts completely out of the fixture and examine them. If there is any scaly (light grey) deposits, that would be the problem.
The solution is to soak all the parts in vinegar, which will dissolve the mineral deposits. It takes awhile to dissolve what has taken long to build up, so heat the vinegar, or put it all on a warm, not hot, surface to keep it more active.
I had this problem, and after cleaning it a couple of times with vinegar, I changed out the Delta to another brand. You could also use a water softening unit, which replace calcium and other metals with sodium, thus eliminating the mineral deposit problem.

the problem is probably not in the actual head but in the valve body where the diverter is attached. It is easy to google something like "how to change the washers on a faucet" and you will find step-by-step instructions on how to do so.

http://www.dummies.com/how-to/content/how-to-replace-a-washer-in-leaky-faucet.html

Do you have stop valves that are built into the faucet body? Some newer faucets have stops built into the unit on each side of the manifold. Make sure they are open. If you don't, then remove the guts from the manifold body and have someone turn the water on slowly to make sure you don't have something clogged. Also depending on the style have cartridge like guts and can be put in upside down. I'm not sure what you have and I wouldn't know even if you gave me the model number. If this fails, you need to contact the manufacturer. They usually have an 800 number that you can call. Good luck!

Usualy when this happens you need to change out the cartrage that controls the water. try to find your faucet at the link below. If you find it click on it scrol down and you can view the manual. It will terr you how to change it out.

http://www.deltafaucet.com/bath/index.html#tubshower_

Good Luck