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Differential Setting

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Posted by Dan on November 16, 2010 at 19:57:46:

I have an old steel boiler and is used for heating only--gas fired water boiler. When cycling, supply water coming out of boiler run 170-180 and return 156-160 degrees when measured with a hand held thermometer. Control is a L8054A Honeywell dual aquastat. Adjustable internal limits set at Hi Temp 180, low temp 120, and differential set at 5. Boiler gauge shows internal temp at 175-180 and approx. 22PSI when cycling (12 PSI of cold static pressure). I thought it may improve efficiency to allow the water to cool to 160 before the burner reignites so I bumped the differential up to 20(the max) but it did not change the operation in any way. I can not find a manual on the aquastat which could have been wired wrong when an upgrade to the AC system required a change out of thermostats. Am I misinterpreting what the differential setting is suppose to do? Is 20 degrees differential to much for a steel boiler? I checked the HW site to see if I can find a manual on the controls but they say that is obsolete and don't have it. I have read many of the aquastat post but most seem to apply systems that are used for DHW and heating so I haven't figured it out yet--not even sure why I need a low limit on my system?

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