Out here, hot water depends on more than the tank. Plenty of properties run on propane instead of a gas main, some are on well water that carries extra minerals through the tank, and many have long runs from the heater to the far bathroom. A Fallbrook water heater is part of a larger setup, so diagnosing one takes somebody who understands the setup, not just the tank.
The warning signs are the same as anywhere, like water that's cooler than it used to be, hot water running out early, a pilot that keeps going out, or rust or moisture at the base. Out here, though, there are more possible causes. Mineral heavy well water can scale a tank faster, propane setups have their own parts that can fail, and the distance the hot water travels changes how warm it is at the far end of the house. So the call starts with your property, what it runs on, how old the tank is and what's changed, and that helps the person who comes out understand your setup.
You'll get a straight answer. If the tank is in good enough shape that a repair does it, that's what you'll hear. If its age and condition point toward replacement, you'll hear that plainly, with options that fit your setup. A licensed contractor can size it for your property and install it properly. The decision is yours, and you can make it at your own pace.