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How to Properly set Aquastat for Summertime Hot Water Production?

ktccapo Member Posts: 35
I have an oil-fired steam system run with a Honeywell VisionPro 8000 with Redlink, utilizing a wireless equipment interface module. The system also provides domestic hot water utilizing an external holding tank with circulator, and an Aquastat L4006A controller.

The temperature on the Aquastat is currently set to 130, with a 10 degree differential. The boiler almost always fires whenever hot water is called for, and now that's it's warmer outside, we're noticing that some of the radiators are getting warm during the hot water call.

Should the Aquastat be adjusted differently? Could the way the Aquastat is wired to the equipment interface module have something to do with when the boiler fires for hot water (much more frequent than before the install of the Redlink system)?

Any advice and/or suggestions would be much appreciated. Many thanks and best,



  • ktccapo
    ktccapo Member Posts: 35
    Good morning, many thanks for your response. In trying to make sense of this for myself, I'd just like to present an alternative viewpoint expressed by some others here on the forum, in that the solution lies in actually adjusting the temp up, but the differential DOWN.

    Does that make sense to you?

    I've attached a few photos of my system. Thanks again and best,


  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541
    You can raise the water level above the level of the coil during the summer, quite a few tankless coil boilers have a large portion of the coil above the usual water line
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