I would like to emphasize that in a problem that arose with the product, within the warranty period, the store's response was immediate. The communication was very good. I highly recommend it.

I declare myself completely satisfied with the product, having lived with it for some time now.

My previous heater was also from Eheim, for several years, but it was from the Jaeger series with manual calibration. Based on reviews, I decided to switch to the electronically controlled one, also considering the price, as the difference from the manual one was very small.

The Thermocontrol E came pre-set at 26 degrees, I simply installed it and when the aquarium reached a stable temperature, I checked it with a glass thermometer and it was exactly 26 degrees. I have checked it several times since then and the reading is always the same. So everything is good. Also, I no longer have the insecurity of accidentally moving the orange ring of the Jaeger and ending up setting a different temperature than I want, essentially losing the true knowledge of whether the device is properly regulating the temperature and has suffered any damage.

I really like the dual-color LED indicator that changes from green to red depending on whether it is heating or not, so I know exactly if it is functioning or not (something I couldn't know with the Jaeger) and if it is heating.

The double suction cup is great, which is not surprising since the company has been producing quality products for many years.

I still have to see its lifespan. The fact that it is a product from the same manufacturer is a guarantee but also a heavy legacy. Jaeger heaters are very sturdy constructions and the bar is set very high. I will update in due course.
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Update 11/02/24
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Just today I realized that the heater is not working. So we are talking about not even 15 months.

Therefore, I am deducting one star. I am not deducting a second one (even though the lifespan was very short) because the company provides a 3-year warranty for the device, which is a significant advantage for me.

It should be noted that the aquarium operates behind a 2kVA OnLine APC UPS. So we can remove the "power quality" factor from the equation.

In an open aquarium of 155 liters with good flow, it keeps the temperature steadily at the level I have chosen without fluctuating if the temperature drops at night, etc. Very good, I recommend it.