Heater switching to different temperatures by itself?

[aquaretem]

I have been using a Eheim Jager 200W heater on a 63gallon/240liters tank for a couple of days now, and something really weird is happening.

The first day it heated the water up to 77ºF/25ºC (it took almost ten hours to reach that temperature), turning itself on and off every minute during the process, shouldn't be turned on constantly until it reaches the desired temperature?

Anyway, it finally reached 77ºF/25ºC and kept the water at that temperature during hours, so I was happy with that. However, this morning, the water went down to 73,4ºF/23ºC, and the heater is now mantaining this new temperature.... So that's the weird thing, how is the heater initially mantaining one temperature (77ºF/25ºC) and now mantaining a different one (73,4ºF/23ºC)?

Also, the initial process it did to get to the desired temperature was normal? Shouldn't be the heater turned on until it reaches the desired temperature instead of being constanly turning on and off during ten hours?

[billdogg]

Heaters are, by far, the most failure prone piece of equipment in the hobby. It is entirely possible that the one you have is just not working properly. I have used the same brand for years and just replace them every couple years as a precaution. Many in the hobby use a controller to help prevent malfunction. At the very least, you will be much better served by using 2 (or 3) heaters of fewer watts so that if one should fail, the chance of it destroying the tank is minimal.

I would return the one you have and try again with another.

[aquaretem]

Heaters are, by far, the most failure prone piece of equipment in the hobby. It is entirely possible that the one you have is just not working properly. I have used the same brand for years and just replace them every couple years as a precaution. Many in the hobby use a controller to help prevent malfunction. At the very least, you will be much better served by using 2 (or 3) heaters of fewer watts so that if one should fail, the chance of it destroying the tank is minimal.

I would return the one you have and try again with another.

Returning it is probably what I will end up doing, but I'd like to know if that behavior is normal or not, in regards to the heater turning on and off instead of being constantly running until it reaches the desired temperature.

[mcgyvr]

Returning it is probably what I will end up doing, but I'd like to know if that behavior is normal or not, in regards to the heater turning on and off instead of being constantly running until it reaches the desired temperature.

No its not normal behavior..

However if the flow around the heater is very low it could be heating up locally and shutting off till the water mixes enough and the localized temp goes down again.. But I really doubt that..

[billdogg]

I would expect it to stay on until it hits the target temperature. Perhaps more importantly I would consider a large drop in temperature to be indicative of failure.

Sorry I wasn't more clear on he first time!

[snorvich]

Heaters fail. Get a controller such as ranco. Using more smaller heaters is preferred.

[Flaring Afro]

A surprisingly large amount of heaters actually do that. This is because they are "preset to a certain temperature" but actually just turn on and off on a regular interval with no sensing of the actual water temperature. Obviously this doesn't work because the preset doesn't factor in the exact volume and ambient air temperature etc. It took me a while to find a heater for a 5 gallon tank that I put a small mantis shrimp in that actually sensed water temp.

This is mostly the ones for smaller tanks though and yours shouldn't be behaving this way and definitely is defective. Just thought I'd mention that for people running small nanos that come up with this in a search.

[mcgyvr]

A surprisingly large amount of heaters actually do that. This is because they are "preset to a certain temperature" but actually just turn on and off on a regular interval with no sensing of the actual water temperature. Obviously this doesn't work because the preset doesn't factor in the exact volume and ambient air temperature etc. It took me a while to find a heater for a 5 gallon tank that I put a small mantis shrimp in that actually sensed water temp.

This is mostly the ones for smaller tanks though and yours shouldn't be behaving this way and definitely is defective. Just thought I'd mention that for people running small nanos that come up with this in a search.

No.. A preset heater is simply set to a preset temperature and does not allow you to adjust it.. It does not function differently from a normal heater.. Its just preset to 78 or whatever (basically the adjustment dial is removed) and still senses the temp via the bimetallic strip or whatever in that specific model.
I have NEVER seen a heater that had no temp sensing and required no external controller.. (maybe they exist but I've never seen/heard of them)
But there are numerous "preset" heaters.. 50-200W+ that are just as I described.. but they do sense temp.. They just don't allow you to adjust the set point.

Now there is also "PID" type control,etc.. where a specific heater/controller may cycle on/off in an effort to avoid overshooting the set temp as set by the hysteresis,etc.....

[Flaring Afro]

No.. A preset heater is simply set to a preset temperature and does not allow you to adjust it.. It does not function differently from a normal heater.. Its just preset to 78 or whatever (basically the adjustment dial is removed) and still senses the temp via the bimetallic strip or whatever in that specific model.
I have NEVER seen a heater that had no temp sensing and required no external controller.. (maybe they exist but I've never seen/heard of them)
But there are numerous "preset" heaters.. 50-200W+ that are just as I described.. but they do sense temp.. They just don't allow you to adjust the set point.

Now there is also "PID" type control,etc.. where a specific heater/controller may cycle on/off in an effort to avoid overshooting the set temp as set by the hysteresis,etc.....

Yes, for extra small aquariums it actually is the most common. The Aqueon Mini Heater is an example.

[mcgyvr]

The Aqueon Mini Heater is an example.

yep.. sure enough.. no internal temp control at all.. Just an always on..
Thats stupid IMO... and too many reviews with people cooking their small tanks with that silly thing..

[PBAF]

More heaters have broke on me than any other piece of equipment. They are definitely disposable. Fish break them, the electronics go bad. Sometimes in as little as a year or two.