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Aquastat Differential

tomstcyr Member Posts: 1
I have a cold start boiler with a Honeywell L8148c Aquastat. The built in 15 degree differential seems to cause the boiler to cycle frequently (not quite a "short cycle" but about every 2-3 min on a cold day). I'd like to adjust the differential to 20 degrees, but this aquastat doesn't appear to be adjustable in that way. Is there a better option?


  • STEVEusaPA
    STEVEusaPA Member Posts: 5,787
    The basic problem is you boiler is making more hot water than is needed. 5 degrees on a differential isn't going to help.
    How many zones?
    Indirect/tankless coil or separate water heater?
    If this is gas, the only way to correct is a properly sized mod con, ODR, and possible a buffer tank.
    If this is oil, then only a buffer tank will help with short cycling.
  • MikeAmann
    MikeAmann Member Posts: 475
    edited November 2021
    Or get rid of that antique aquastat. The new controllers do so much more and are programmable to do things that can't be done with switches, timers, and relays. Ask me how I know? I am about to place my order tomorrow with Supplyhouse.com. The excellent advice from the pros here helped me see the light.

    Or you could add an Intellidyne HW+ Fuel Economizer to your current aquastat which will hold off the burner from firing if the water in the boiler is hot enough to satisfy the call-for-heat. Essentially, this increases your differential - up to as much as 60 degrees. This is what I am abandoning because the new controllers have this function already built into them. But I do love my HW+ and it works great. It has saved me 30% for the last 10 years.
    If you are interested in going the HW+ route, I have 2 of them that I will no longer be needing - 1 new in the box. Are you afraid of a little wiring?