How does an aquastat really work?


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Old 12-09-10, 09:08 PM
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How does an aquastat really work?

I have an old Crane cast iron boiler in our 4plex(i'm the owner). The Grundfos pump crapped out and was replaced today. My plumber adjusted the aquastat at 180F on the hi side and 120F on the low. That is a 60F difference but he told me that the pump will still run as long as the units call for heat. Does that mean that the boiler will start its cycle at 120F and shutdown at 180F? Is this a good range or would you rather the range be narrower? I live in Western Canada so it gets alot colder than most parts of the Americas. If I can save a few dollars on the gas bill so that the boiler does not cycle every 10 minutes would be good but could there be problems with that thinking too?
 
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Old 12-10-10, 07:30 AM
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I have no knowledge of boilers, but with that kind of swing the boiler will cycle less, not more.
 
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Old 12-12-10, 10:49 AM
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My plumber adjusted the aquastat at 180F on the hi side and 120F on the low. That is a 60F difference but he told me that the pump will still run as long as the units call for heat. Does that mean that the boiler will start its cycle at 120F and shutdown at 180F?
First of all, I am not a boiler expert, but the aquastats I have had experience with did not affect the boiler control at all and were simply a thermostat that controlled the circulation pump according to the temperature of the water in the hot water storage tank. That being the case, you could expect the pump to run continually trying to satisfy the high temp 180 degree setting because I doubt the boiler temperature is set as high as 180 degrees. If it is, you could expect to have 180 degree hot water at the tap and that is a very scary thing to think about! In my opinion, the maximum setting should never be above 140 degrees maximum or you would risk scalding temperatures. If the problem has to do with the water not heating quickly or sufficiently, you may have a scale buildup problem in the heat exchanger coil that needs to be addressed.
 
 

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