Heater cycles on and off ~20 times per hour

[fish4phil]

I have a Fluval M300 300 watt heater in my 75 gallon. FX6, ambient room temp is 69. Heater is set to 82. Fluval says the M300 is good for up to 80 gallons.

The heater turns on for about 20 seconds, then turns off for about 2 minutes. And repeats this all day. I work in the room the tank is on and hear the audible click every time it cycles on/off.

I read posts where other heaters turn on/off 10 times a day, not 20 times an hour.

Is this normal? Why such short cycles?

 

[ColdKoi]

The only reason a heater would be short cycling is that it’s either too large for the water volume or the temperature switch is too sensitive.

I tend to go with undersized heater running fairly steady. In an efficiency standpoint it’s better and will last longer (less switching)

I run a 200w in my 75g with about a 10-15° delta also and it only turns on once or twice an hour for less than 10min

 

[Aiken Drum]

I really liked my M series fluval heater that came with my Roma tank. Its was by far the most reliable heater ive had and wish i could buy replacements. The only M series heater i can source here in the UK is the 50 watt.

Could be a faulty heater, or could be its positioned in an area with incorrect flow (too much/ too little). Have you tried moving the heater somewhere else in the tank? I position heaters vertically, close to the filter intake.

Does the heater give you a steady temperature in the tank?

I certainly didnt hear a clicking when my M series heater turned on/ off which makes me think there is a fault. The problem with what its doing is that the switch will wear more and fail quicker. If it happens to fail in the on position it will cause overheating if you arent watchful or it happens overnight.

 

[Colin_T]

The heater is coming on a lot because the room is colder than the tank temperature. This is causing the water to cool a bit and the heater is trying to warm it back up.

If you insulate the base, back and sides of the tank with 1-2 inch thick polystyrene foam sheets, it will reduce the heat loss and the heater won't have to come on as often. A decent coverglass will also help trap heat. Use 4, 5 or 6mm thick glass because it traps heat more than the thinner 2 or 3mm thick glass sold in pet shops and is less likely to chip or crack.

Make sure the aquarium isn't near an external wall. Cold air can radiate off external walls and cool aquariums down very quickly.

Have the room door shut to help stabilise the temperature in the room. It can help reduce the cold air coming into the room and cooling things down.

 

[fish4phil]

Thanks all. Heater is vertically oriented right next to the filter intake.

Aquarium is away from windows and any exterior wall. The wall behind the tank does not contain any HVAC venting.

The temp throughout the tank is consistent and does seem steady.

Maybe it's a faulty heater. I'll try to replace it.

Would a 200W heater be better, aka hold temp longer and stop cycling so frequently?

I run a 200w in my 75g with about a 10-15° delta also and it only turns on once or twice an hour for less than 10min

10 to 15 degree swings through the day depending on the heater's cycling? Isn't that fairly extreme?

 

[Aiken Drum]

300w heater seems right for your size tank. 1watt per litre (4 watts per gallon).

Undersized heaters run for longer and this will reduce their lifespan. There is also a risk of it not being capable of getting your temperature up depending on the difference between your room temp and tank temp.

Ovetsize heaters will flick on and off more frequently. Again this will reduce their lifespan.

No substitute for having the right size heater.

 

[fish4phil]

300w heater seems right for your size tank. 1watt per litre (4 watts per gallon).

Undersized heaters run for longer and this will reduce their lifespan. There is also a risk of it not being capable of getting your temperature up depending on the difference between your room temp and tank temp.

Ovetsize heaters will flick on and off more frequently. Again this will reduce their lifespan.

No substitute for having the right size heater.

Awesome! So if 300 watt sounds right for a 75 gallon, does it sound right to you that it flicks on and off about 20 times an hour?

 

[Aiken Drum]

Thanks all. Heater is vertically oriented right next to the filter intake.

Aquarium is away from windows and any exterior wall. The wall behind the tank does not contain any HVAC venting.

The temp throughout the tank is consistent and does seem steady.

Maybe it's a faulty heater. I'll try to replace it.

Would a 200W heater be better, aka hold temp longer and stop cycling so frequently?



10 to 15 degree swings through the day depending on the heater's cycling? Isn't that fairly extreme?

I think coldkoi means there is a 10 to 15 degree difference between room and water temperature. Although i do get that much temperature swing in the winter between daytime when the room is heated, and nightime when its not.

 

[Aiken Drum]

Awesome! So if 300 watt sounds right for a 75 gallon, does it sound right to you that it flicks on and off about 20 times an hour?

No. My M200 on my 200 litre came on 2 or 3 times per hour for 2 or 3 minutes each time. But your heater is maintaining a constant temperature, so is doing its job. Either the thermostat is too sensitive or your tank quickly loses temperature and brings the heater on very rapidly.

You might want to invest in a good thermostat controller like an inkbird. You can just set the heater to a higher temperature and let the thermostat device do the control side.

 

[fish4phil]

No. My M200 on my 200 litre came on 2 or 3 times per hour for 2 or 3 minutes each time. But your heater is maintaining a constant temperature, so is doing its job. Either the thermostat is too sensitive or your tank quickly loses temperature and brings the heater on very rapidly.

You might want to invest in a good thermostat controller like an inkbird. You can just set the heater to a higher temperature and let the thermostat device do the control side.

That's a good idea with the thermostat controller!

 

[ColdKoi]

10 to 15 degree swings through the day depending on the heater's cycling? Isn't that fairly extreme?

No. 10-15° delta. The difference between room temp and tank temp. It holds steady with the 200w, cycling only a couple times an hour for a short period of time.

I agree if you had an issue with your hvac and the house temp dropped significantly it likely would have no chance of maintaining tank temp

I originally planned to run 2x 200w heaters. One set at 78 and the other a few degrees cooler. That way if one heater fails the tank temp won’t drop significantly and I don’t have 2 heaters cycling steady. But every time I go to the shop all they have are little heaters!

In an efficiency and longevity standpoint a heater that runs constant is going to be more efficient and last longer than one that cycles steady. So keep them in good water flow and don’t get too carried away with the size

 

[Andy Sager]

Thanks all. Heater is vertically oriented right next to the filter intake.

That could be part of the issue. Move the heater away from the filter or away from the intake. The filter is constantly pulling water from all over the tank so cooler water, water that is furthest away from the filter, is constantly being passed by the heater and that may be what is causing your heater to be constantly clicking on and off. What I would do is place the heater by the filter outlet so that the warmer water is being distributed throughout the tank. If doing this does not change the frequency of the ons and offs, then I would really consider having the heater checked out for any faulty parts.