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An immersion heater is a device that is installed in a container to heat a liquid. Not every type of immersion heater has a replaceable thermostat, but some do. If you need to replace an immersion heater thermostat, the best one to choose is one that is certified safe for use in the system for which it is intended. If possible, choose the same brand of immersion heater thermostat as was originally installed.
If you are planning to buy an immersion heater thermostat, check for a ratings tag. There are several major certification organizations operating around the world, and the ratings tag will tell you which agency evaluated the device. An immersion heater thermostat will be evaluated for safety based on the elements used, which might include things such as copper, stainless steel or a hybrid nickel-iron-chromium metal. The agency also will have evaluated the flange materials, the conductivity elements that ensure an adequate current from the electrical socket to your heater, and the quality, durability and lifetime of the heater. A non-certified immersion heater thermostat from an unknown manufacturer might overheat and cause the thermostat wire to melt, which is a common problem and one that can lead to dangerously overheated water and even electrical fires.
Immersion heaters come in several varieties, such as ones that heat water in a cup for tea or coffee while traveling and ones that screw into the side of an electric or gas hot water heater to heat water for washing, bathing and cleaning. There also are immersion heaters for industrial and commercial applications, such as those that keep water in a stock tank from freezing or those that operate heat transfer systems. For the most part, these do not have replaceable thermostats. Immersion heaters are also manufactured to keep the water in a hot tub or spa warm, and these do come with replaceable thermostats.
If you're choosing an immersion heater thermostat for your hot tub or spa, you shouldn't buy a “knockoff” or “one off” brand. Choose, if possible, the same brand of immersion heater thermostat that was originally installed. Very often, the seller will offer replacement parts for the products it sells. Some manufacturers also allow consumers to order replacement parts, or you can check with an electrical supply parts retailer or search on the Internet for a seller. Be sure to check whether your thermostat was covered by a warranty, which might entitle you to get a replacement for a lower price or even for free.