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Under tank heater


alanmin4304

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I have just set up a tank 1200 L X 425 W X 400 H and used a 300 watt heater from Argos with a love TS temperature switch. It is set for 25deg C with initial water temperature of about 10 deg C and ambient around 15 deg C. It has about 50mm sand in the bottom. I have had to add another element/thermostat to get the water temperature up as it did not want to get above 15deg after 2 days. Is this normal--- any suggestions welcome as this is my first experience with these heaters. I have tested the element by putting a light bulb in the circuit and it is OK.

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Hi Alanmin,

I'd suspect the element is not coming on. If in two days the water temp has only come up to the ambient and won't go any higher it means the heater is not working or the thermostat is incorrect.

300W should easily pull the tank up to 25'C in two days:

300W x 60sec x 60min x 48 hours = 51MJ

204L x 4200J/'C x 15'C = 12.85MJ

So, it should have been up to temp even with 75% energy loss...

Must be the thermostat if the heater is showing as ok. Did you plug the light bulb into the thermostat output and turn the dial to see if the setpoint is correct?

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The thermostat is electronic and reads the actual temperature (which is correct when checked against an electronic thermometer) but you preset it to the temperatue you want. I slightly damaged the aluminium cover on the heater when putting the tank in place and tested the element direct by putting the current through the heater then a light bulb to check that the circuit was complete, and it was OK. The thermostat has 2 connections for the probe, 2 for power in and 2 for power out and I think I have it connected correctly. I think I will disconnect the additional heater and see what happens. When I got it made I thought 300 watts would be way more than required, it surprised me that it took so long to heat up. I will check the output connections to see if they are OK.

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If you turn the thermostat up and down now as it swiches on and of that should be the present water temp Does this correspond to the temp on the thermostat. leave turned up slightly and leave and see if it raises the temp and turns of again.

Cheers

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Got it sorted, the thermostat was cleverer than me. It can be set to refrigerate as well as defrost and once I got it set to heat rather than cool it all fell into place. To pass on the info---I have made a 1200 tank divided into 6 compartments and the temperature of the central 4 are within 0.1 deg and the end ones about 1.0deg less (heat loss I guess). That is with the water level the same and tested with a digital thermometer.

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