The answer to 'when to service water heater' is that you should have your water heater serviced at least once a year, or more frequently if you notice any issues. Regular maintenance helps ensure your water heater is operating safely and efficiently, and can extend its lifespan.
During a water heater service, a technician will typically inspect the unit, flush the tank to remove sediment, check the anode rod, and test the temperature and pressure relief valve. They may also adjust the temperature setting or make other minor repairs if needed.