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Heat Switched Off, but Radiators Warm with Calls for Hot Water

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,



  • Steamhead
    Steamhead Member Posts: 16,283
    There should be some way to keep the boiler from getting hot enough to make steam when only the hot water is calling. The aquastat on the tank does not do that.

    Post some pictures and let's take a look at it. Also, where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • ktccapo
    ktccapo Member Posts: 35
    Good morning, thanks for your response. You've also been responding to a similar post I have over in Domestic Hot Water.

    If not the Aquastat, then what exactly does determine calls to the boiler for hot water? Other than a faulty Aquastat and/or circulator, what could be causing the boiler to make steam (get too hot) during a call for hot water?

    Could there be a problem with the internals of the boiler itself?

    In the photo I attached, you can see the Aquastat, the circulator, and the low-water cutoff.

    Thanks and best,


  • ktccapo
    ktccapo Member Posts: 35
    Many thanks for all of your help, adding water to the boiler was indeed the answer. No more heat creeping up into the radiators on hot water calls.