Why is My Aquarium Heater Blinking?

Why is My Aquarium Heater Blinking?

Heaters are critical equipment to maintain the tank’s water temperature and overall environment, including the fish health.

Why is My Aquarium Heater Blinking? An aquarium heater can start blinking when it does not receive enough power supply and can not stay ON for a long time. Moreover, any problem with the thermostat, such as its burning or improper indication, causes problems. Other equipment in the tank, like filters and light sources, also interrupt the heater working, making it flicker.

Good quality and expensive aquarium heaters always come with an indicating light of different colors.

Why is My Aquarium Heater Blinking?

The light is necessary to understand whether your heater is properly working or not, helping you to keep the water warm as required.

Sometimes, you will observe the flickering of these lights, stressing you about your fish: it can happen any time and because of any reason, so always keep an eye on every piece of equipment on your tank.

The heater blinks due to a light indicator issue, or most probably, it has some internal damage, leading it to flicker. 

Insufficient electrical supply

A heater is an electronic device that requires a constant supply of energy or current to run efficiently.

When the power supply to the equipment decreases, fluctuations in current increase, leading to abrupt working and blinking.

Broken cords and wires, improperly plugged-in, or damaged power outlets are responsible for insufficient current supply.

Always double sure after plugging in the heater and before placing it in the tank, check the bucket of water whether it is getting enough power.

Also, if your power outlet or switchboard is not working correctly, never plug in the heater in it: it may spark a fire or destroy the heater at once.

Rapid cycles of aquarium heater

The term rapid cycle means abnormal heating patterns of the heater, which occurs when it does not remain on and off for a longer time.

Broken parts or damaged heating components are the reasons behind rapid cycles. Moreover, it is not appropriately sized equipment for your aquarium.

You should place the heater submerged in the water if it doesn’t support this feature; otherwise, it can cause problems.

As a result, the water remains cold, and you have no benefit of having a heating source in the aquarium.

Bring it up slightly so the heating component remains in the water and the upper body comes out of the water.

I recommend contacting a professional for its repairing if there are any changes. Otherwise, it is time to replace it with a good one and never use it even as a spare device.

Never choose a powerful and big heater for your aquarium. The size and power capacity of equipment should correspond to the tank size.

Damaged heater

In the case of the cheap and low-quality heater, you will experience misoperations, or one day you will see it dead.

While some equipment starts indicating before they completely stop working, blinking is one of them.

It shows you that the heater is not receiving energy or processing heat as a response to burn or worn-out internal parts.

Quality is the key to longevity, therefore do proper research and ask for guidance before purchasing.

The problem with the thermostat

The thermostat regulates heat production by a heater in an aquarium.

Any problem with the thermostat has a direct effect on its heating. For example, the heater will not get any start or stop indication from the thermostat.

Sometimes, it burns and starts working abruptly, and you can not identify it from outside unless blinking starts.

Moreover, when you place a tall heater vertically, in a way that the thermostat is at one point and the heating element on the other, it may flicker.

The blinking increases when you have high water flow in the tank, and the thermostat can not read the actual temperature of the water.

Place it according to the installation guide and with great care to avoid a mishap: place a submersible one fully submerged in water and keep it away from the wall or substrate.

The light indicator is about to fuse

Usually, the filter can last for 3 to 4 years if they receive proper care and maintenance, but the indicator may trip early.

In addition, these light have a specific life and starts to dim with time and starts blinking.

Short-circuit or current fluctuation is often responsible for the early fusing of indicating light in an aquarium heater.

Other light sources in the aquarium

All the equipment in an aquarium affects each other, whether it’s positive or negative.

You may often notice that the light blinks when the aquarium lights are off, and it stops blinking when aquarium lights are on.

The phenomenon is that the other light sources in the tank impact indication lights, making them work weirdly.

When you newly install the heater, the electrical waves produced by other equipment in the tank impact these new electrical devices.

Electric current from the filter

The current produced by the filter passes along the water through the heater make it flickering.

Turn off the filter for a while to see if the problem is occurring due to filter current but never turn off the filter for a long time: it is critical to the fish health.

Once you detect the problem, try to decrease the flow rate a little and see if it improves.

The blinking of the aquarium heater is normal in some cases

Sometimes, the flickering of the heater light is normal, and there is nothing dangerous about it.

Typically, the light blinks when there are slight changes in current flow and becomes normal when you switch it OFF for few seconds.

Moreover, light and other reflections in the tank make it appear blinking but are not.

Blinking over several days is not a big deal but if it continues for a long time, look for the cause and solution. You should know about the different types of aquarium heaters.

What does the light on the aquarium heater indicate?

Indicating lights reduce your load by making you aware of the heating situation from outside of the tank: look at the equipment if it is ON, the heater is producing heat.

These lights are ON and OFF periodically in response to the water temperature inside the tank.

This periodic blinking is an indication of activated or inactivated equipment. 

The working and non-working stages of heaters correspond to the set aquarium temperature to prevent overheating or underheating. 

What are the different colors of light used in aquarium heaters for indication?

Aquarium heaters come in a variety of different light colors, functions, and heating controllers and regulators.

Red light

Red light is standard in many aquarium heaters; that seems to be dangerous but is not.

The red lights show that it has not reached the required temperature and is still heating. Do not worry and let it do its work.

Once the temperature reaches a goal, the light will automatically turn OFF, and the device will stop heating.

The required temperature is the temperature you set manually on your equipment, which is suitable for tank inhabitants.


Greenlight is a good indication, telling you that your fish tank heater has achieved its goal and reached the set temperature.

However, it will also turn OFF after some time with turning OFF the equipment to prevent overheating of the heater.

 When the temperature starts decreasing in the tank, it will automatically turn ON until it reaches its goal and the cycle keeps going on.

White light

Some heaters have a bright white light that appears to be an indication in their equipment.

This light is generally the arc that forms when the electrical bending of metal over another closes some points to allow electricity to flow through the heating component to produce heat in response to cool water.

The same happens when the water gets warmer, and there is a need to open contact points to prevent electrical flow.

The white light is typically the flashlight that evolves at the time of heaters turning ON and OFF.

Neon light

Neon gas is rarely seen in any brand now and appears slightly amber or orange in color shade.

It is neon gas filled in a glass tube that brightens up when the device is working.

Blinking is usual with neon light, might be during excitation of electrons of gas or some other unknown reason.

However, LED lights are more popular nowadays. This is because they do not flicker and last long.

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