Trouble with Eheim Jager 300w

  • #1
I picked up a second hand 800l (210 Gallon) tank a few months back and it came with an Eheim Jager 300w heat. The tank was running when I purchased it and the heater must have been working correctly but I'm having issues keeping the temperature stable. After setting up the tank I had a massive temperature spike and took the Eheim heater out and and replaced it with an spare Elite heater I have. The Elite heater isn't ideal for my setup.

Since then I have tested the heater in a large bucket and found that the heater is about 5 degrees off from the indicator. I made adjustments to the temp and got the bucket of water stable at 25C or 77F. The heater was functioning perfectly and kept perfect temperature with no fluctuation. So I put it back in the tank and monitored the temperature. Day one the temperature climbed to 27C or 80F and looked reasonably stable. The second day I notice the temperature had gone up to 29C or 84F and have unplugged it.

Doesn't any one know why the heater would hold a stable temperature in one body of water and not the other?

There are a few factors that could be affecting this from what I can see. I've listed the three option below:

Option 1 - The heater is broken

Option 2 - The lack of movement in the water in the bucket could have a different affect to that of the filtered water in tank. Though I don't think this would make a material difference.

Option 3 - The electrics on the tank are coursing a problem with the heater. In the bucket I had the heater connected directly to the mains but in the tank there are built in electrics. Light and pumps are working fine though and I'm no expert on electricity. I am taking a shot in the dark here.

Note: I'm certain the problem isn't coursed by lighting and I'm in the southern hemisphere and we are currently in winter. Outside factors can be ruled out, although the room the tank is in gets very cold over night.

  • #2
Jägers have to be calibrated in the tank itself. I've two of those and gave me a hard time to do so. Try to get a manual from the internet and do so. When set correctly they are great !!! To my believe : You've to unplug it, turn the red point to de actual temperature and then turn the blue to the temperature you like. Don't understand eheim/jäger wasn't able to make this easier to do.

  • Thread Starter
  • #3
Thanks DoubleDutch,

In my 300l tank I have another Eheim Jager that sounds the same as yours. You have an adjustable marker to compensate for the heater being out a few degrees. My problematic heater I think is an older version and doesn't have this. It wouldn't make a difference though as I've managed to set the heater to work at 25C in the bucket of water and this should technically be the same in the tank but something is throwing it off.

Any other guesses or opinions?
  • #4
Okay. Yeah you'd would expect it only to stay under 25C in your tank.

Sorry I don't know the older ones !!
  • Thread Starter
  • #5
I've got the Hester running at its minimum setting and the tank looks stable at 24C. The safest bet I'm thinking is to get a replacement. Will have to hold out until next pay day though.

Sent from my ETAB M7023G using Fish Lore Aquarium Fish Forum mobile app
  • #6
how are you setting up the jager? they are meant to be put in sideways not standing up right
  • #7
When set correctly they are great !!! To my believe : You've to unplug it, turn the red point to de actual temperature and then turn the blue to the temperature you like.

Hi, I have the same problem with my brand new Eheim/Jäger in an all new aquarium (new startup).
No fish yet though.

What I don't get is the part when I turn the red point to the actual aquarium temperature (28C) but I want it to be on (24C).
The red arrow can't even BE turned more to the right to hit 28C without turning the blue ring to the left!
It's a stop on the backside that prevent this from happening.

When calibrating - I unplug, turn the red point to 28C (the present water temp.)
and then the blue BACK to the red arrow (24C). But I still have 28C after 24 hours, and the sensor starts and heat the water up as soon it drops below 28C.
I don't want it to go decrease over 24C!
So how do I calibrate that?!

I want the heater to be sturned off so the water will cool off and drop to 24C by itself, and THEN turn on and regulate it to wanted 24C.

Can someone please help me to get it right??

Thank you!

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