How To Tell if Aquarium Heater is Broken? These Things Can Help!

Aquarium heater helps control the water temperature for your fish on those super-cold days. Many fish lovers, me as well, may know how useful this heater is, but sometimes, we might confuse if the aquarium heater is working or not.

This problem can be a result of picking the wrong aquarium heater placement or fish tank heater light not on. And which way can let us know that aquarium heater light on but not working?

I had fallen into this kind of situation many times before, so now I want to help you guys prepare a better environment for your fish. Let's discover how to tell if aquarium heater is broken or not!


Aquarium Heater Guide for Very Bginners

If you have known this information, you're welcome to skip this and move to the next part: how to tell if aquarium heater is broken.

1. What is an aquarium heater? Is heater necessary for aquarium?

When deciding to have a fish tank in your house, you should consider about aquarium heater first. Fish can't produce their body heat as human and mammals. Therefore, they need relying on the water temperature to maintain a better status.

An aquarium heater controller will help you keep the proper degree for your pets, especially if you've lived in a low-temp room with lots of tropical fishes.

2. Which kinds of heater are suitable for your fish tank?

Following these standards to pick the right heater:

Types and where to place aquarium heater

Submersible heater: This type of heater will be set under the water, next to a filter to warm up all the water flow into the tank.

  • Hanging heater: It's also known as Immersion heaters. This type will be attached on the top of the tank, while the heater part sits in the water increasing the tank's heat.
  • Substrate heater: This type is quite expensive when it supports other heaters to make the water flow more gently. Substrate heater usually in the form of wires and should be fixed onto the tank base.
  • Filter heater: A kind of filter that has heating function built-in so that it will heat all water runs through the filter.
  • In-line heater: This type can be set inside the sump or the canister filter to heat water up on the way back into the tank.

An all-in-one submersible aquarium heater can help to maintain the right temperature for the fish

Choose the right aquarium heater’s size for your tank

Aquarium heaters have many sizes which you can choose based on the room's temperature and volume of the tank.

You can follow the aquarium heater size guide on this table:

Aquarium Size

Heating Required

9 degree F

18 degree F

27 degree F

5 gallon

25 W

50 W

75 W

10 gallon

50 W

75 W

75 W

20 gallon

50 W

75 W

150 W

25 gallon

75 W

100 W

200 W

40 gallon

100 W

150 W

300 W

50 gallon

150 W

200 W

200 W x 2

65 gallon

200 W

250 W

250 W x 2

75 gallon

250 W

300 W

300 W x 2

This table show which types of aquarium heater will suitable for each size of a fish tank

For example:

  • Your room's temperature is 60 degrees F
  • You want the tank to reach 78 degrees F
  • Heating required is (78-60) = 18 degrees F.

In this case, if your tank size is 5 gallon, you will need a 50-watt aquarium heater

Similarly, 25-gallon tank needs a 100 watt aquarium heater, 40-gallon tank needs a 150 watt aquarium heater, 50-gallon tank needs a 200 watt aquarium heater, 65-gallon tank needs a 250 watt aquarium heater, and 75-gallon tank needs a 300 watt aquarium heater.

3. Fish tank heaters how they work?

Aquarium heater will turn electricity into heat and maintain the preset temperature for the fish tank.

When the water's temperature is lower than needed, the aquarium heater will automatically turn on itself to heat the water.

Do fish tank heaters turn off automatically?

When the water reaches the preset temperature, the heater will automatically turn off itself. Therefore, you don't need to worry about getting high temperature aquarium heater that’s not suitable for your fish.

4. Best aquarium heaters you can choose


A submersible aquarium heater is stuck on the tank base to warn up the water for the fish

  • Aqueon submersible aquarium heaters: This heater has red and green lights to show if it's working or stopping automatically. Beside, Aqueon heater is shatterproof and updated to one more temperature accuracy.
  • Fluval aquarium heater: Fluval heaters can show the exact temperature in Fahrenheit and Celcius degree along with advanced warming technology to protect the fish.
  • Marina aquarium heater: Marina heaters don't have innovative functions, but it is effortless to use and set up into the tank.
  • Tetra HT submersible aquarium heater: Tetra heaters are suitable for those with a tight budget. This heater has enough essential function in a compact size, which is convenient to put anywhere in the tank.
  • Top Fin aquarium heaterTop fin heater can provide you with the exact temperature along with a double layers design to distribute heat evenly.

How to tell if aquarium heater is broken tutorial

You will need:

  • A thermometer: to check the temperature outside and inside the tank
  • A bucket with 10 litres of water: to test the heater performance

How to tell if aquarium heater is broken

Step 1: Check the light while running your aquarium heater

  • Turn on your aquarium heater.
  • Check the light on the heater.
  • If the fish tank heater light not on, it might be a kind of Stealth heater with a metal body, so you cannot see the light go on or off.
  • In case the aquarium heater light on but not working, you can check if the heater broke or not with the next step.

Step 2: Use a thermometer or your hands to compare the temperature


You can know how to tell if aquarium heater is broken or not by using a thermometer to compare the fish tank’s temperature

With a thermometer:

  • Put a thermometer into the tank before running an aquarium heater.
  • Let it run and see if there is any change from the water's temperature.
  • Make sure your tank is not affected by the sun or fish tank's lights while testing.

With your hands:

  • Your thermometer sometimes can give you the wrong result. So you can testing with your hand carefully.
  • Wash your hand first and then put it into the tank.
  • Move slowly toward the heater.
  • If you can feel hotter as soon as you get closer to the heater, it's not broken.
  • If you don't feel any change in the temperature, you might touch and hold the heater without getting burnt.

Step 3: Figure out if the aquarium heater working automatically

  • Determine the temperature of your room and water in the fish tank
  • Set the heater with a higher temperature comparing to the water
  • Put the heater back to the tank (follow how to place heater in a fish tank with each type of aquarium heater)
  • Check other signs like: is the light turns on, is the water heating up, etc.
  • You can use a torch to illuminate the water flow around the aquarium heater. If the heater is working, it will blur everything next to it like a fire so you might see the water movement under the light.

Step 4: One last check with a smaller space


Figure out how to tell if aquarium heater is broken by testing the heater once again with a water bucket

  • How long does it take for a fish tank heater to heat up? It needs at least one day or 30-36 hours to warm up a tank. That's why you need to experiment on a small space to save more time
  • Find a bucket with 5-10 litres of water inside
  • Again, determine the water's heat before and after placing an aquarium heater
  • Also, check the light and the water movement like step 3
  • The total waiting time should be at least 30 - 60 minutes.

Why isn't my fish tank heater working?

All the steps above can help you to confirm if your aquarium heater is still working and if the answer is "No", you might know the reason why it's broken in these following cases:

1. It's a defective product

If your heater is a brand new one, try to test it with the instruction of step 4 as soon as possible.

You can get a new one from the store if the product has a problem right at the beginning and it's not your fault.

Make sure you have checked the heater carefully and still eligible for the store's returning policy.

2. It's not an excellent heatproof appliance

Your heater can be an all-glass aquarium heater or made with other materials that don't withstand high temperatures.

When the room temperature lows down and your preset warmth for the heater is higher, it might be over the aquarium heater temperature range.

The different degree can lead to not working status or breaking the heater directly.

3. You might forget to unplug the heater while changing water for the fish tank


Don’t forget to unplug the heater every time changing water for the fish tank

Many people make this mistake when using an aquarium heater.

Along with heatproof things, changing the water temperature immediately while the heater is working can make it easier to broken.

In another situation, you can let the water drop into the plugin location and break it right away. Or even worse, you might experience an electric shock.

4. It needs a rest

Maybe your aquarium just went through a super hardworking time, so it needs a period to recover.

Besides, if it has followed you for years, it's time to find a new aquarium heater protecting your fish.

Can a fish tank heater catch on fire?

Things can catch on fire easily in a fish tank usually are the heater, the filter, and the lighting because they have electric inside.

An aquarium heater can overheat and explode the glass tube that let many heater elements out and can catch any flammable things to start a fire. Otherwise, this scenario is quite hard to happen because the heater and its wire are designed to heatproof and submerged in water, which nearly cannot catch on fire.

What to do when the aquarium heater broke and how to prevent it from recurring?


You should use a multi-way socket instead of a handy power bar to prevent the outlet from getting wet when you’re cleaning the fish tank

  1. Don't try to fix it yourself: Regardless you're handy or not, when a heater broke, it shouldn't be fixed or reused to protect your fish.
  2. Buy a top-quality heater and a spare one: A heater is essential for your adorable fish. So buy a good heater to keep your fish in good condition and a spare one to reduce the damage.
  3. Get an aquarium heater cover: This heater guard can prevent the heater from contacting directly with all the glass wall, aquarium decoration, and your fish.
  4. Follow the installation and usage direction: Make sure you put the heater in the right place and use it in the right way to maintain the heater performance.
  5. Make a regular cleaning schedule: Clean your heater, lighter and filter regularly to remove all the salt creep, which can affect the quality of those appliances. Don't forget to unplug them when cleaning the fish tank.
  6. Use a multi-way socket instead of a handy power bar: A fish tank with at least three electrical equipment will need more outlet than a standard wall socket can offer. You might get a convenient power bar to solve it, but it might be dangerous if there are water drips from the tank. That's why a multi-way socket will be safer for your house.


All the tips above saved me from panic when my aquarium heater died, and I hope these can help you too. Not everyone falls in the same situation as me in the beginning if ones know how to secure a heater and keep the fish safe.

Now, how about you? Tell me about your cutest fish and how to tell if aquarium heater is broken in your case. If you don't agree with the given solutions, feel free to leave your opinion in the comment section below. It the end, it all for our fish, isn't it?

FAQ: How to tell if aquarium heater is broken?

1. Are aquarium heaters safe?

The aquarium heater is safe for use. The unsafe part will only happen if you didn’t do as what the precaution said. 

Problems with a fish tank heater maybe: malfunction, break or electric burn - a result of overuse or let the water meet the outlet.

2. How long does a fish tank heater take?

It usually needs 24-48 hours to reach the preset temperature. After two days, if the heater cannot reach that level, you should check if it’s still working (follow the instruction above) or consider buying one more heater for a large tank.

3. Can you submerge aquarium heater?

You can submerge the aquarium heater into the water, based on its type and function.

There are five main types of heaters with different areas to place, so if you choose a submersible heater, you can sink the whole heater under the water. Or if you go with an hang-on heater, only the heating part will be submerged in water.

4. How to place heater in fish tank?

This part also based on the aquarium heater type. An immersible heater requires a hole in your tank’s hood to keep this heater in the right place, and others will usually submerge in the water.

You can stick them on the tank wall with their vacuum pads (should be attached horizontally in the lower part of the wall) or put them on the tank base.

The best position is placing the heater vertical near the inlet (filter, pump, etc.) to adjust the water temperature from the beginning.

5. How to fix aquarium heater?

If you find out your heater is not working properly, you should try to place and turn it on one more time, or other testing methods to see if it’s only malfunctions or totally broken.

Next step is bringing the heater to the seller or fixer. You shouldn’t try to fix it yourself since it might cause more danger to you and your fish.

Let the professionals do the work or buy a new heater.

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3 thoughts on “How To Tell if Aquarium Heater is Broken? These Things Can Help!”

  1. Thanks for sharing the great article with us. In this article, you shared detailed information about heaters. Patel Heaters and Control Pvt Ltd also deal with the same industry.


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