My enclosed shower/tub combo hot water knob just spins & won't turn the water on...I popped the front cover open to tighten the screw only to find that it is stripped (my son had being turning it on/off like this for some time but failed to tell me!) Can I just change out the stripped screw & knob with new ones without turning off the main water supply? I've got the needed materials, I just have no access to the back of the shower 😜 & not sure if I remove the stripped screw & faucet without turning water off first, will it spray a fountain of water into my face or will it be ok ? Thank you for any help or advice. I'm pretty handy with most home repairs, just haven't done too much plumbing by myself & have nobody to ask.
Every shower handle and regulator is a bit different.
See the picture below which is just an example:
If you are really just replacing the handle - which is really items 1-4 (and sometimes 5-6 or sometimes 5-6 don't exist) - then no you do not need to turn off the water. But just by the nature of doing this you are probably going to move the stem and get sprayed with water off and on, or just on if I am doing it.
As every manufacturer is a little different there are various reasons why handles get loose. This example shows a more gears/bushing connection, some manufacturers use a specific shape (square/rectangle/hex) to connect the handle.
The reason why I not this is sometimes 5-6 is stripped and the handle is fine. And sometimes 5-6 is really part of the main regulator and as soon as you start moving them water starts coming out of 8. So if you are sure you are just putting on the handle you do not need to turn off the water. But once you start touching other things turn off the water and turn on the faucet at the lowest point in your house (this will help drain the lines so you don't get a half gallon of kickback in your walls).
As a side note: Turning off the water for your house should be a simple process of turning a valve. You should not be scared to do this and this is good practice as you might need to turn it off in an emergency situation. All adults living at a house should be OK with turning on/off the water and power to house. Also the bathroom or shower could have its own shutoff valve. For a shower this would usually be the floor below and sometimes (not often) under the sink.