You go to turn on your fish tank heater, and nothing happens. You check the plug and make sure it’s in the right spot, but still no heat. Then, why isn’t my fish tank heater working still? Don’t worry, you’re not alone. Heater malfunctions are one of the most common problems with fish tanks. But before you run out and buy a new heater, there are a few things you can check to try to diagnose the issue. In this article, we’ll go over the most common causes of an aquarium heater not working, as well as some tips on how to fix them. By the way, if you’re looking to boost your online presence, you might want to Get Youtube Subscribers. 

    The Wrong Size Heater for Your Tank

    The size of your tank is a key consideration when purchasing a fish tank heater. If your tank is too small for the heater you’ve chosen, it’s not going to work properly. In fact, you might even damage your fish tank and its inhabitants by using an undersized heater.

    You need to make sure that the heater you select is the right size for your tank. If you’re not sure, consult the manufacturer’s guidelines or speak to a specialist retailer.

    Incorrectly Installed Heater

    If your fish tank heater isn’t working, the first place to check is to make sure it’s been installed correctly. Tank heaters need to be completely submerged in the water in order to work properly, and they must be covered by a layer of insulation to prevent heat loss.

    If your heater is installed improperly, it may not be getting enough water to operate correctly. This can lead to the heater becoming too hot and melting or causing a fire.

    Heater Not Compatible With Other Tank Mates

    One of the more common reasons why a heater might not be working is because it is incompatible with the other tank mates. If you have a large tank, for example, and you try to use a small heater, it might not be able to generate enough heat to keep the entire tank warm.

    Similarly, if you have fish that require cooler water temperatures, using a heater that is designed for warmer water will not work. Be sure to check the compatibility of your heater with the other fish in your tank before making a purchase.

    Heater Not Compatible With Substrate

    One of the most common reasons your fish tank heater might not be working is because it’s not compatible with the substrate in your tank.

    Substrate is the material you use to line the bottom of your tank, and it can be made of anything from gravel to sand to rocks. If your substrate is too thick, it can block the heat from getting to your water.

    To fix this, you’ll need to either remove the substrate or replace it with something that won’t block the heat. You might also need to get a new heater that’s specifically designed to work with thicker substrates.

    Debris in the Tank

    If there’s debris in your tank, it’s possible that it’s blocking the heat from getting to the water. This is especially true if the debris is blocking the heater’s intake or output.

    To fix this, you’ll need to do a thorough cleaning of your tank. First, remove all of the water and then disassemble the tank. Clean all of the parts with warm, soapy water and a soft cloth. Be sure to rinse everything thoroughly.

    Once everything is clean, reassemble the tank and fill it with fresh water. If the debris was blocking the heater’s intake or output, you should see the heater working now.

    Algae Growth on the Heater

    clear glass fish tank with blue fish

    If your fish tank heater isn’t working, one of the common causes could be algae growth on the heater. Algae can prevent the flow of heat and cause the heating element to overheat, which can damage the heater.

    To clean the algae off your heater, simply turn off the power and remove the heater from the tank. Then, using a soft brush or cloth, gently scrub the algae off the heater. Once you’ve removed all the algae, rinse the heater off with clean water and put it back in your tank.

    Aquarium Not Covered

    One of the most common reasons your aquarium heater might not be working is because the aquarium isn’t covered.

    Yep, you read that right. A lot of people think that as long as the water is touching the heating element, it will work. But that’s not always the case.

    If your aquarium isn’t covered, the heat can escape, and your heater will have to work overtime to try to make up for it. So make sure your aquarium is covered!

    Water Level Too Low

    underwater photography of fish and corals

    If the water level in your tank drops too low, it can cause your fish tank heater to stop working. This is because the heating element in the fish tank heater is designed to be completely submerged in water in order to work properly.

    If the water level in your tank drops below the heating element, it will cause the element to overheat, and this can cause permanent damage to your fish tank heater.

    To avoid this, make sure to keep a close eye on the water level in your tank, and top it off as needed. You can also invest in a glass or acrylic canopy for your fish tank, which will help reduce evaporation and keep the water level more stable.

    Tank Not Cycled

    One of the most common causes of a fish tank heater not working is that the tank isn’t properly cycled. The cycle is a biological process that’s essential to keeping your fish healthy, and it involves bacteria breaking down ammonia and other toxins in the water.

    If your tank isn’t cycled, it means there aren’t enough beneficial bacteria present to break down the toxins. This can be a big problem, because it means your fish are constantly being exposed to harmful ammonia and other chemicals.

    To fix this, you’ll need to cycle your tank. This can be done by adding a bacteria starter kit to your tank, or by using live plants. Once your tank is properly cycled, you should see a significant reduction in the toxins present in the water, and your fish will be much happier and healthier.

    Thermostat Malfunction

    photography of aquarium with corals

    The final common cause on our list is a thermostat malfunction. If your heater doesn’t seem to be kicking on at all, it could be that the thermostat isn’t working properly.

    A thermostat is what tells the heater when to turn on and off, so if it’s not working, the heater will never turn on. This can be a tricky problem to diagnose, so it’s always best to consult with a professional if you suspect this is the issue.

    How Do I Know if My Aquarium Heater is Working

    If you’re not sure whether your aquarium heater is working, there are a few telltale signs to look out for. One is that your fish will be noticeably more active than they were before. Another is that the water will be warmer to the touch. And finally, you might also notice that the water is less cloudy than it was before.

    What Are the Signs That My Aquarium Heater Is Not Working?

    If you are not getting the desired results from your aquarium heater, it is likely that it is not working properly.

    Here are some signs that this may be the case:

    • The water in your tank is not getting heated to the desired temperature.
    • The water in your tank is cloudy or has a film on it.
    • Your fish are swimming close to the surface of the water.
    • Your fish are swimming in groups near one corner of the tank.

    How Often Should I Check My Aquarium Heater?

    orange guppy fish

    You should check your aquarium heater at least every other day to make sure it’s still working properly. If you don’t, you could end up with a tank full of dead fish.

    To check your heater, first make sure the tank is unplugged and that the water is cool to the touch. Next, remove the heater from the tank and submerge it in a container of water. If the water in the container is hot, then your heater is working properly. If the water is cool or cold, then your heater is not working and you need to replace it.

    How Do I Troubleshoot My Aquarium Heater?

    If your aquarium heater isn’t working, the first thing you should do is check the power cord to make sure it’s plugged in. If it is, then you’ll want to test the outlet to see if it’s getting power.

    Once you know the outlet is working, the next step is to check the thermostat on the aquarium heater. Make sure it’s set to the correct temperature and that the light is on. If everything looks good there, then you’ll want to check the fuse.

    If the fuse looks good, then you’ll need to replace the aquarium heater. I know, it sucks when something like this happens, but at least now you know how to troubleshoot it. By the way, you can learn how you can heat your fish tank without a heater on our other blog posts.

    How Can I Prevent My Aquarium Heater From Breaking?

    Here are a few things you can do to prevent your aquarium heater from breaking:

    • First, make sure you’re using the right size heater for your aquarium. If the heater is too small, it will have to work overtime to heat up the water, and this can cause it to break.
    • Second, keep an eye on the temperature of your aquarium. If it starts to get too hot, turn off the heater and let the water cool down.
    • Third, clean the heater regularly. This will help prevent it from getting clogged with dirt and debris, which can cause it to break.

    Frequently Asked Questions:

    Why is it essential for a fish tank heater to work correctly?

    A functioning fish tank heater is crucial for maintaining a stable and comfortable water temperature for your fish, as temperature fluctuations can stress or harm them.

    What are some common signs that my fish tank heater might not be working properly?

    Signs of a malfunctioning heater include fluctuating water temperatures, water that is too hot or too cold, or a heater that remains off despite being plugged in.

    What are some potential causes for a fish tank heater not working?

    Possible causes include a faulty thermostat, a damaged heating element, an incorrect heater size for your tank, or electrical issues.

    How can I troubleshoot a fish tank heater that’s not working correctly?

    You can troubleshoot by checking the thermostat settings, verifying the power source, inspecting the heating element for damage, and testing the heater in a separate container.

    What should I do if I suspect that my fish tank heater is not functioning correctly?

    It’s essential to address the issue promptly to prevent harm to your fish. Isolate the affected fish, perform water changes if necessary, and either repair or replace the heater.


    In short, there are a lot of potential causes for an aquarium heater not working, but the most common ones are a lack of power, a failing thermostat, or a build-up of sediment.

    If your heater isn’t working, the first thing you should do is check the power supply. Then, if it’s plugged in and the power is on, then the next step is to check the thermostat. If the thermostat is set too low, then the heater won’t turn on. Finally, if there is a build-up of sediment on the heating element, then that can prevent the heat from being conducted properly.

    If you’re still having trouble, then the best course of action is to consult a professional. They will be able to diagnose the problem and get your heater up and running in no time. Why isn’t my fish tank heater working? We hope you’ve been able to provide a reliable answer to your question.