How do I know if my aquarium heater is working?

Check for an indicator light (most heaters have an LED that shows when heating). Use a separate thermometer to verify actual water temperature matches the set point. If the heater light stays on continuously or the temperature does not match, the thermostat may have failed. A stuck-on heater is dangerous — replace immediately.

Can an aquarium heater kill my fish?

A malfunctioning heater stuck in the on position can overheat water to lethal temperatures. This is the most common aquarium disaster. Prevention: use heaters with auto-shutoff (Neo-Therm), dual sensor protection (Fluval E), or use two smaller heaters so a single failure raises temperature less dramatically. Always monitor temperature with a separate thermometer.

Best Fish Tank Heaters 2026