6 Aquarium Heater Problems and Solutions

Aquarium fish are extremely delicate pets to have. They need routine monitoring, water changes, adequate oxygen supply, water heating, and much more. An aquarium heater is a crucial gear to keep the fish alive and well.

For harsh cold winters, an aquarium heater is essential. Oftentimes, aquarium heater causes issues that are vague for general people to understand.

So, what are some aquarium heater problems and their solutions?

Aquarium heater problems include overheating, smoking, light blinking and flickering and not turning off. For heating problems, check the thermostat and the heating coil. Replace or fix them as necessary. For blinking and flickering problems, it indicates the heater has a problem. Replace the heater.

Need more detail? We provided a detailed solution in the article. Now you can stop your frantic Google searches and read this article for solutions!

Water Heater Problems: Is It An Actual Problem?

Before you proceed to solve your aquarium heater problems. Let’s see if your aquarium heater has problems or if you need to adjust a few things. 

  • First things first, check if the heater is properly plugged in. 
  • Check the water temperature with a thermometer. If the temperature is equal to or above your pre-set temperature. The heater is not working because the water is at the right temperature.
  • Check the fuse, it may need replacement if the heater isn’t working.
  • If you’re using digital heaters, check and replace batteries.
  • Check the heater for any physical damage
  • Check if the heater wattage is adequate for the amount of water in the aquarium.

If you have checked everything off this list and still facing problems, keep reading to the next section.

Aquarium Heater Common Issues and Fixes

1. Aquarium Heater No Thermostat

Aquarium heaters with no thermostat are difficult to find nowadays. And we’d strongly advise you against getting an aquarium heater without a thermostat.

Although aquarium heaters are very inexpensive, they are also heavily unreliable. And if you have this type of heater, keep reading for the solutions to problems you’re facing.

If you are having problems with your heater that has no thermostat. Don’t try to fix it at home. The wise decision is to buy a heater with a built-in thermostat.

2. Aquarium Heater Too Hot

Your aquarium heater is too hot to touch. Or, the water of the aquarium is getting too hot.

The reason behind this problem is either a fault in the built-in thermostat of the aquarium heater. Or, the heating coil is faulty. 

Internal Thermostat Problem of the Aquarium Heater

The thermostat presets the temperature. It self-regulates the temperature based on the given command on the temperature range.

If the thermostat is broken, the aquarium gets too hot or too cold. 


Pull the thermostat out and check the wiring. Alternate the wiring and that should fix your thermostat and aquarium heater.

The easiest and most inexpensive solution is to purchase a separate heater and use it.

A thermostat that uses different lights to indicate the temperature range. Getting an LCD screen is more convenient. It will show you the temperature of the water.

Green signifies the temperature is within range, and a red light indicates that the water is too hot. The temperature is lower when the light is blue.

Faulty Heating Coil

It typically consists of a glass shield and two to three heating coils made of steel. After extended use, they corrode, lose efficiency, and eventually stop functioning.

Mold develops inside the heating coils due to excessive moisture in plant leaves and other detritus.

Aquarium heaters can overheat the tank as a result of corrosion. Extreme temperatures stress fish, making them more susceptible to illnesses. To keep the coils dry, adequately insulate them.


Replace the heating coil. You can easily do it by measuring the size of the coil. Try to buy a nichrome coil because they are highly resistant to corrosion and high temperature. They can withstand up to 1200F.

3. Aquarium Heater Smoking

The aquarium heater smoking is never a good indication. It means it emits excessive heat. This could happen for many reasons.

First. You have turned on the heater before putting it in the water. Or there’s a sudden power surge and short-circuit problem. The glass heater may have broken which is creating smoke. 


The solution to the smoking problem isn’t complicated. If your heater glass has broken, immediately stop using that aquarium heater. Buy a new one for replacement.

Do not attempt to fix the crack with adhesive. The heater could potentially explode. In which case you’ll lose your pets.

Turn the heater off and take it out of the aquarium. Let the heater cool down completely. Then gently place it inside the aquarium at an angle. Wait 20-30 minutes. Then turn it on and let the temperature rise gradually.

Remember to turn off the heater before you change the water of the thermometer.  

4. Aquarium Heater Blinking

The aquarium heater blinks because it’s not getting enough power supply to operate. It could also be that the water is cycling too fast which is interrupting the heater’s operation. 

The light indicator may also be close to a fuse. Or there are other problems with the heater it’s indicating. 


Check the bucket of water to make sure the heater is receiving adequate electricity. Do this after plugging it in and before placing it in the tank.

Additionally, never plug a heater into a broken power outlet or switchboard. Since this could immediately start a fire or damage the heater.

5. Aquarium Heater Light Flickering

If the aquarium heater is flickering, it is indicating a problem that needs immediate attention. It could be that your submersible water heater is above required the water level. 


Turn your heater off immediately. Check if the light is fusing or not. Next check the socket and plugs to see if they’re in working condition. Submerge the heater till the required water level.

Change the water heater to keep your pets safe. 

6. Aquarium Heater Won’t Turn Off

If the aquarium heater is not turning on, either the heater has expired or there could be another problem. For instance, the light switch is stuck, or the switch is broken.


If the switch is stuck, replace the switch. Replace the light indicator of broken. Buy a new aquarium heater if you’ve been using this heater for a long time. 


How Do I Know If My Aquarium Heater Is Broken?

A simple inspection method can tell you if your aquarium heater is broken or not. In a steady motion, draw your hand towards the heater. If your start to feel the water getting warmer in your hand, heat is emitting. And the heater is working. If you can touch the heater with no trouble, it’s broken.

Do You Need To Fully Submerge Your Aquarium Heater?

Some heaters need to be fully submerged, others don’t. Aquarium heaters are made waterproof. And they either stay full or halfway submerged. There’s a line on the aquarium heater that tells you the minimum requirement for submerging the heater. However, fully submersible heaters are more popular.

Why Is There A Red Light On My Aquarium Heater?

A red light on the aquarium heater is nothing to panic over. It indicates that your heater is working and heating the aquarium, not the other way around. Green light means it’s on stand-by mode. To let you know the aquarium heater’s work status, the manufacturers install indicator lights. 


That was all about the aquarium heater problems and their solution. You should be able to figure out your heater problems from the solutions I discussed above. Keep your fish safe and best of luck!

Howard Parker

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