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Oil Furnace not circulating - pipes hot, but not drawing through pipes

webclicks Member Posts: 2

I have four zones which are not drawing hot water. The water for taps/shower is hot but no hot water is circulating to the rads. This behaviour is inconsistent, the last time it occured the water did not circulate until 8-12hrs until after I noticed the problem. Now it's reoccuring again. What should I look for?

I highlighted the parts are hot to the touch:


Back area:



  • Jamie Hall
    Jamie Hall Member Posts: 21,526
    My first question would be...is that pump actually running? And if not, what is supposed to make it run? But that's the first thing to look at.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • webclicks
    webclicks Member Posts: 2
    The pump will run, it wasn't at the time of the post. For instance the hot water started circulating in all zones a few hours after this original post.

    I'm sure it'll become unresponsive again, but I don't know why.
    HVACNUT Member Posts: 5,250
    Open the aquastat cover (grey box at the top rear of the boiler). What are the settings?
    If there's only one dial, it should be set between 160°- 180°. If there are three dials, Hi, Lo, and diff, then the Hi must be set at least 20° higher than the Lo. Since you have an electric water heater, the diff can be set to 30.

    If all looks correct in the aquastat, try turning off the power, then back on. If that gets the circulator running, then it could be a faulty aquastat.