Common reasons for no hot water in your house include a faulty thermostat, a broken heating element (for electric heaters), or gas supply issues like a pilot light failure (for gas heaters). Check your thermostat setting, reset tripped circuit breakers, and relight the pilot light if necessary. 

Replacing a water heater typically costs between $800 and $3,500, depending on factors such as the type (tank vs. tankless), size, energy efficiency, and installation requirements. Consider consulting a professional for accurate estimates and to discuss the best options for your home.