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Discussion Starter · #1 ·
I got a 100 watt Marineland VisiTherm for my 20 gallon a 2 months ago to replace a Whisper HT30 with an inaccurate preset thermometer. For the past couple months it has kept the water at 76F right where I want it with absolutely no variation despite the fact that it occasionally gets as low as 60F in the house at night. I was astonished when I checked the thermometer on the tank yesterday evening and discovered the water was the same as ambient, 65F, meaning the heater was no longer heating the water despite the light being on. I put the only spare heater I have on hand right now in the tank (250 watt VisiTherm) and placed the 100watt VisiTherm in a 1 gallon jug of water to verify that the heating coil was bad. To my astonishment it is heating the water despite being on the same setting as it was in the tank--76F. The water from the tap is up to 67.6F from 64.5F when poured and climbing. I'll check it in a few hours and see where its at but this just doesn't make sense.

I am supremely irritated with this heater and I've already ordered a 100Watt Eheim Jager to replace it but I'd still like to know what is going on. What does it all mean?
 

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This is a very common way for heaters to fail. When I tear heaters down to see how they have failed, I often find it is not the heater coil but the controls which fail. Many heaters have tiny little contacts smaller than a 1/16" square mounted on a metal plate. This metal plate is made of two metals which expand and contract at different rates. As the heat kicks on/off the one metal plate gets larger than the other side so the plate bends just slightly. This movement makes the tiny contacts come together or move apart turning the power on or off. You can see that this little metal plate is not real strong and has little power. The problem comes up when the power switches on and there is a tiny little arc at these contacts. This arcing can soon weld the contacts together and the heater sticks "ON" or it can burn the contacts and the power doesn't pass through.

My theory on what your heater did? The contacts burned enough to stop making contact so the heater stopped heating. But then when you moved the heater and set it up, just a bit of the corrosion was knocked off the contacts and they are working until the corrosion builds up again.
I would not trust it to work very long.
 

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Discussion Starter · #3 ·
You're absolutely right about not trusting it, there's no way I'd stick this thing back in another tank. Marineland has a lifetime warranty on their products so I'll probably send it in for another one to keep around as backup only. It really bothers me though because this is the third VisiTherm I have owned and the last couple were rock-steady. Had the first for seven years until I dropped it by accident and the second one I received free with a tank a friend was giving away six years ago and that one is still working. The temp never matched the settings but once I got them dialed in it was always set it 'n forget it.

After fiddling with it for awhile now it works again but the actual temp is ten degrees above the set temp or more. Plus there's something rattling around in there which I'm sure isn't normal. Maybe the VisiTherms have taken a quality control nose-dive or something.
 

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If you've not taken a heater apart to look, do a check of my posting about what's in your heater. The temperature setting being off after a heater has failed once is somewhat easy to explain once you look at the parts. the contacts are often mounted on the metal plate. Once the heat sticks on or off the plate may be bent enough to distort the reading as it can be bent beyond the normal movement it can handle. That can catch new folks and those who really don't want to spend too much more. The heater looks like it works but just a bit off the normal setting so they put it back in the tank with contacts which are semi-burned. It doesn't take long until they burn again and do their dirty work.
 
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