Hi Kathy, the Helio Smart PTC heaters not only have a traditional remote sensor but they also include one inside the elements. When the two sensors are not reading the same temperature an E7 alert will alarm and turn off the heater until reset as this could be a critical risk to overheating the aquarium.
The most common reasons for an E7 could be a water change at different temp, colder ato replenishment water entering near the sensor, or sensor coming out of water. To reset, just push any button on the controller. We advise to keep the audible alert on located on the side of the controller.
The PTC heater will slowly and gradually heat the water back to the desired set temp. So you will be fine in the meantime.
Best Regards,
IM Team