How do you get the plastic body out of a single handle shower valve?

If your new Delta single handle shower valve won't shut off, it could be due to an issue with the valve itself or with the installation. Some possible causes include a misaligned handle, debris in the valve body, or a faulty cartridge. It is best to check the installation instructions and ensure that everything is properly seated and aligned. If that does not solve the issue, you may need to contact Delta customer service for further assistance or consider hiring a plumber to diagnose and fix the problem.

two possible causes. 1- make sure the valve body is installed with with shower mark on the valve body facing up. 2 - if you used pex pipe and fittings to stub out for the tub spout this will restrict the flow sending water to the shower, '' change out pex pipe and replace with copper or galvanized pipe

Sounds like someone did not remove the plastic valve assembly before soldering the valve body to the copper piping.
That or the valve body needs cleaned out. It is common for debris to get knocked lose when doing installations on old plumbing.

Sounds like the delta people forgot to install the diverter piece inside of valve body,small white plastic piece screwed into valve. If you take out valve you should see it up inside body

Moen and all shower valve manufacturers follow american federal guidelines. Hold the unit in your hand with the handle facing you - the left side is the hot water inlet and the right side is the cold water inlet.

On your single handle the first thing you do is remove the handle. To do this locate allen set screw on handle and select the right size allen wrench to fit it. Loosen set screw and pull handle out away from wall to remove it. There should be a plastic disc on the handle stem, slid it out to remove it.Remove chrome sleeve..On valve body there are marking that show hot or cold settings. Seperate teeth on geared flanges and rotate set stop toward h mark on valve body. Each tooth will change temperature about three degrees. Make trial setting and reassemble and try it out. If you want it hotter just repeat adjustments. If you try to go to far you will not be able to mesh gears,simply back off alittle bit and try again.Hope this helps you. Thanks

you can try drilling a small pilot hole and then use an "easy out" (get'em at any hardware store). or take some large pliers and break the plastic handle and remove the whole cartridge. Go get a new cartridge and handle. Make sure main water valve is shut-off prior do doing so though.

You need to pull and replace the cartridge on your shower valve most likely. It varies by Make and Model, but generally, remove the handle, remove any sleeve around the center spine, remove the round trim plate, close the service stops, remove the retaining clip or ring, and pull the cartridge straight out of the valve body by pulling on the spline... or get a cartridge puller. Then take your cartridge to the store and get a new one. Flush the valve body by slightly opening both service stops and then install the new cartridge and reverse the process.
Generally this problem occurs when sediment has torn part of the sealing o ring on the cartridge. If you send me the make/model and/or a picture I will give you the specific instructions

Is this a dual handle or single handle? if it is a single handle
turn the valve 180 degree. if not, then check the cold water supply line.

I need to ask a few questions to solve your problem.

What Model Shower body is it?
How big is the white plastic piece?

If it is about 6 inches around (just smaller than the face plate) and you are installing this shower body in a preexisting tub/shower, this piece can be discarded. It is a guide that is used so the tile contractor knows how much room is needed to service the valve once it is installed.

If this is not the case, just post with a few details and I'll modify my response.