The answer to 'when to service water heater' is that you should service your water heater annually to ensure it is operating safely and efficiently. This involves draining the tank, inspecting the anode rod, and checking for any leaks or other issues. Regular maintenance can extend the lifespan of your water heater and prevent costly breakdowns.
It's also a good idea to visually inspect your water heater monthly for any signs of trouble, such as leaks, strange noises, or discolored water. If you notice any issues, it's best to call a professional HVAC technician to diagnose and repair the problem.