Some heaters were manufactured without a required flame rollout switch, which is a back-up device that shuts down the heater in the event of a heater failure. This poses a fire hazard.
A wiring problem can cause the aquarium heaters to overheat or break during normal use, damaging the aquarium and posing fire and laceration hazards to consumers. Overheating can cause the heater to shatter or the aquarium glass to break.