Keep getting low fluid alarm on new polyscience heater / chiller

Hey guys I am trying to run hot condenser tec and when I get to high temps (above 125c) my polyscience 7L heater circulator errors out on low fluid alarm. Im using carbon chemistry Thermoltec HTF in the bath and when I called polyscience they told me its because when the oil gets hot its specific gravity gets low and causes the float to drop. I looked at polyscience’s site and their recommended oil is a silicone oil thats $1200 a gallon which I would need 2 gallons which is almost as much as the heater was. Anyone have a good heat bath oil that doesn’t cost thousands? But also has a good enough specific gravity not to trip the alarm… Thx guys!

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Wire tie the float up and make sure you don’t run out of oil or you’ll have a nice lab bonfire

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@goldleaf_scientific whats the specific gravity of this product?

syltherm-800-technical-data-sheet.pdf (24.5 KB)

Two settings I modified on my heater, may differ from yours: on the back there is a cross tip screw switch. this is a safety setting that shuts the system down if it goes over a certain temp. Mine was on 90C when I bought my heater. I twisted it to set it past 180C. Second, somewhere there is a setting on your heater that allows you to input a decimal number that correlates to the thermal capacity of the oil you are using. It has presets for distilled water (1) and polyscience branded transfer fluids to make your life easier. Select custom. I’m using Duratherm S and I put in 0.47 into this field. There was a chart on duratherm’s website where I was able to look up the number for thermal capacity at a specific temp. I forget what the number is called or what unit it was in.

Also make sure you’ve filled up your heater with the appropriate amount. Sounds like your heater might be less than half full. You’ll want ~2/3+ full. I bought two gallons and dumped 80% of it into a 7L heater.


I bypassed my float sensor its pretty easy. I can show a pic when I get to it tonight… I was forced to because it would trigger regardless. Its just a wiring thing.

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Can you please detail the bypass? I am having trouble with the same thing on a polyscience with an advanced digital controller. AD15-40 Thanks!

Find the float switch it will have 2 wires going in, connect these 2 wires.