My price pfister tub valve leaks

we would need a little more information but sounds like it will need replacement, The water will eat up the meatle and make a rebuild impossible sorry but no quick fix the hot water lineis usley the culprit

You have to turn water off to shower and remove handle then cartridge lock ring then there are two washers and srpings that can be popped out with small screwdriver.Lowe's has replacement springs and washers ,be sure to mark position cartridge was because that is very important to reinstall the same way it came out.

There may be 2 pins if under ring the collar has multiple holes.remove pins & unscrew ring... or it could be just stuck from age..

I have a single handle price pfister shower valve Model 17196-0100k .No cold water.It's coming hot on both sides.

Hot on left.
Cold on right.
Some single handle faucets have bleed-over where both hot and cold enter mixing valve each time handle is turned on, even when faucet calls for just cold or just hot.
Otherwise maybe a do-it-yourself plumber got pipes backwards... or maybe the tub used to be on other side of wall, and tub was moved during remodeling but pipes were not changed.

To fix problem:
First of all, turn off shower faucet. Turn on Hot at sink and put ear against shower faucet listening for sound of water flowing through the mixing valve.
If mixing valve is working fine, you need to open wall and investigate more.
For example if you have access door, reach in and feel which pipe is hot.
Pipes might need to be reversed if problem comes up in home inspection, otherwise the problem will not harm anything.

If I understand correctly, you have single handled shower faucet.
Normally there is a wait for hot water to arrive at faucet.
But now hot water is already at shower faucet.

Single handled faucets have a mixing area inside valve where hot and cold come together before going into sink.
This mixing valve can have crossover where the hot and cold can pass through to each other even when faucet handle is off. When single handle faucets get old, this can happen.
How it happens:
For example another faucet is turned on inside house, and pressure differential between hot and cold causes hot water at shower handle to pass through mixing area and into cold water line.
So if another faucet has been run, then that lets hot flow to faulty single handled shower faucet.
To confirm this is the problem: turn on other faucet and put ear against shower faucet to listen for moving water.
This condition may also signal there is a water leak.
The problem is not harmful, but will draw cold water into water heater each time, and is energy wasteful.
Replace faucet or have plumber repair problem.

You can cap the lines at the tub faucet to rule out tub faucet. It maybe mixing there.

Faucet may be bad also the safety stop will alow you to change water temp it can be tricky to adjust water temp.

It's likely that you have some sediment that has accumulated in the cold water valve and has clogged it. The model number you have cited above is only for the trim (rather than for the valves behind it). Assuming that you have a Price Pfister valve, they don't have built in filters, so you're probably going to have to either clean or replace the valve.

you must replace the whole stem.you can get it at homedepot. first take the cover off over the stem. this should screw off or is held on with a allen key.then unscrew stem from valve body.make sure water is off to tub,just in case.

This sounds like a proper with your water heater. If you just installed this new shower head. First take it off and make sure that the hot water valve is opening fully if that checks out then go to the water heater and make sure the pipes check out ok and also that the heater is ok. Try putting a water heater blanket on it. Also try getting some pipe cover and cover the hot water line so on really cold days or not you will have warmer water