Heater Not Maintaining Heat?

I'm starting to become convinced this heater is just a piece of .

I have a Tetra HT10 heater in a 10 gal.

It has been working relatively fine since I got it.

Red light on it = heating up to temperature
Green = At the right temp (78)

Today, the light went red. Which is the first time it's done this.

I took it out, ran a test by filling up a bucket, submerging it, and letting it heat up. It took 5 minutes, then went green.

Stuck it back in my tank, it took 5 minutes, went green.

I thought "all is good, it likely shut itself off because it detected some kind of issue".

Well then it went red yet again after an hour.

So I took it out right now, tested, put it back in, and it's green...again.

I checked the water temp and it's at 76 Fahrenheit and is getting back to 78.

Should I be concerned? PetSmart has no problem refunding me, and has before for issues. Should I just leave the heater alone for the rest of the day, stop being paranoid, and see what happens?

 

That's normal for me in my 5.5 gallon tank with the same heater. When the tank temperature drops it turns red to signal it's heating back to 78 and once it reaches 78 again it turns back to green, repeat.

 

If you have any doubts about your heater replace it. Especially if you won't have a problem doing so.

 

From the instructions that came with the unit.

Some heaters include an indicator light that will glow red while
the unit is heating and switch to green (or turn off) when it
reaches the optimal temperature. This light will not be
visible if your heater is installed inside a filter box.

 

Red light on it = heating up to temperature
Green = At the right temp (78)

If the temperature in the tank drops below 78F, the heater comes on and the red light indicates that it's heating. When the tank gets to 78F, the heater stops heating and the light changes to green. Due to the way they detect temperature, it's not unusual for them to cycle on/off a few times before finally hitting 78F and turning off for a longer period.

From everything else you've described, it sounds like it's working exactly as it should. What exactly do you think is the issue?

 

If the temperature in the tank drops below 78F, the heater comes on and the red light indicates that it's heating. When the tank gets to 78F, the heater stops heating and the light changes to green. Due to the way they detect temperature, it's not unusual for them to cycle on/off a few times before finally hitting 78F and turning off for a longer period.

From everything else you've described, it sounds like it's working exactly as it should. What exactly do you think is the issue?

I'm just paranoid. I have fish that are very sensitive to temperature changes, so I was worried the heater was taking a dump and it would entirely stop working and hurt the fish.

My problem was that I believed it would stay on red, and never get back to 78.

I already had a defective heater before, same model, from the same store. It went red, I waited a day, checked everything, and finally the light went off and it died on me.

Thankfully, the heater is working fine. I was just paranoid, thinking I was going to have the same issue AGAIN.

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Any thermostatically controlled device will have some level of hysteresis -- in this case a temperature fluctuation required before the device turns on. Some level of hysteresis is desirable in this application since you don't really want the heater rapidly turning on and off every time the tank cools by 0.01F. If the heater doesn't come on until the actual temp is 1.0F below the set point, then the heater is going to run for a while before the tank gets back up to the target temp.

If the temp drops a couple degrees below the set point then you may have something to be concerned about.

I would also add that unless you have discus or something that really requires very warm water, it's likely your fish will do fine at room temperature. Nature doesn't provide them with as steady a temperature as most fish keepers do, yet fish seem to generally do fine with natural temperature swings. Unless your room is very chilly, I wouldn't panic if the temp drops a couple degrees.