I dropped my hairdryer and it hit the toilet shut off valve. The oval shapped valve broke off - it looked like it was connected by plastic and some putty - probably some patch up job from the previous homeowner. Is it easy to replace just the knob?

If the stem isn't broken it is just a matter of removing the screw and what is left of the handle, and buying a new handle. If the stem is broken, It is more difficult. You have to shut the water off somewhere else, unscrew the nut at the base of the stem and pull the whole works out. I find a place such as an Ace Hardware or True Value are more like to have the part you need and somebody to help you find it than the big home centers.

You could decide to leave it go until if and when you need to work on the toilet. Even then, you could just use pliers on the stem to close it.

If ''elsewhere'' is the incoming water, you will have to shut off the heat to the hot water tank unless it has an expansion tank. Water expands when it is heated, and usually goes back out the inlet.

Thanks this helps a lot.