Many people after installing a UV water lamp are surprised to notice that when there is no water flow—for example, at night or during prolonged absence—the sterilizer becomes hot. This post will teach you a few important things:
The reference model here is Nordic Tec UV water lamps equipped with Philips bulbs. We invite you to read on.
All light emits some heat, and this is a normal physical phenomenon, regardless of the manufacturer of the UV water treatment system.
UV light does not emit heat like, for example, infrared radiation, and its ability to heat water is limited compared to other methods. With regular flow—meaning frequent use of tap water—the water temperature practically does not change or is heated so minimally that it is barely noticeable.
What happens then? In this case, water exposed to UV rays for a very long time may warm up, which is a completely natural phenomenon. The UV sterilizer may then feel hot to the touch, which worries many people—however, this is not a dangerous phenomenon. It also only affects a very small volume of water—specifically, the water directly inside the UV sterilizer—which is why, when turning on the tap in the morning, you may briefly feel warm water. That’s essentially all there is to it.
Yes, the fact that a UV lamp becomes hot when there has been no water flow for many hours is natural and safe for the system.
Water heating by UV rays has very natural limits and cannot damage the sterilizer or the bulb. UV lamps (provided they are high-quality products) are inherently built from materials resistant to higher temperatures and temperature fluctuations. Additionally, the glass covering the bulb is not ordinary glass but made of quartz (glass with a high silicon content, offering much greater durability).
First and foremost, water in a UV lamp cannot boil for simple reasons—and these are the laws of physics. All light, including UVC rays, has measurable heat, meaning heating potential. In the case of UV lamps, it is impossible for water in the sterilizer to boil because UV light cannot heat it to such temperatures.
Admittedly—after many days of stagnation in a UV filter, water can reach significant temperatures—even 60-70°C, which we perceive as hot or scalding when touching the lamp’s steel chamber. However, UV lamps are designed for such temperatures, and this is no cause for concern. It is still insufficient to damage the system.
There is even less reason to worry about potential damage to the plumbing, as it is important to remember that only a very small volume of water is heated—only the water directly undergoing sterilization.
No, you should absolutely not turn off the UV filter when residents are at home. There is no justification for this—it does not risk overheating, and moreover, frequently turning the lamp on and off is not recommended (it neither benefits the bulb’s lifespan nor helps maintain a barrier against E. coli bacteria or other microorganisms entering the water system). It is not advisable to turn off the lamp at night, while away at work, and certainly not to install water flow sensors that activate the bulb. This would damage it very quickly (unless we are talking about LED lamps).
The situation is different, however, when you are away. For absences longer than 1-2 days—such as weekend trips—it is highly recommended and may even extend the bulb’s lifespan in the long run. In such cases, it is also wise to turn off most electrical devices in the house.
UV lamps are safe and properly protected against temperature fluctuations. Water heating by the lamp is possible in some cases, but there is no need to fear it. Under no circumstances should this be a cause for concern, as it lacks the potential to damage the sterilizer.
Hot water in a UV lamp is not harmful—in fact, paradoxically, the barrier of hot water at 60-70°C creates an insurmountable obstacle for bacteria and microorganisms, so it certainly will not hinder the main goal of using this product: clean water at home.
✅✅ This article refers to Nordic Tec UV sterilizers, which are treated here as the reference model. We emphasize that each product and manufacturer may have its own specifications and intended use. Therefore, for definitive recommendations regarding the topics discussed in this text, please refer to the user manual or contact the manufacturer or distributor of the specific product directly.
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