Sudden changes in shower temperature deserve attention. Pressure-balancing and thermostatic valves provide different forms of temperature protection; their function depends on the product and how it is installed and adjusted.
Ask a qualified plumber to evaluate the existing fixtures and recommend an appropriate solution. Installation and temperature adjustment should follow the product manufacturer’s instructions. Do not assume that every valve provides whole-house protection or increases the amount of hot water available.
If you notice unexpectedly hot water or abrupt temperature changes, discuss the concern with a plumber. A home inspection can identify observable plumbing concerns, but it does not certify that every fixture prevents scalding.