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3-Zone Heating Issue

jneilan22 Member Posts: 2

I have a steam boiler that serves radiators on floors 1 and 2 of my home. We did a renovation of both floors in 2017 and the plumber installed a "cheater loop" using a Taco 1/25 HP Cast Iron Circulator pump to create 2 new zones of hot water baseboard heat off the same steam boiler. Zone 1 serves the first floor and Zone 2 serves the second floor. The cheater loop is a regret, but we're stuck with it at this point.

The zone for the steam heat works as expected off the steam heat thermostat. The Zone 1 heat also works as expected of its thermostat. The problem I am having is that the Zone 2 heat has 2 problems: 1) when the thermostat for Zone 2 is set, it kicks off the circulator pump (as it should) but it also generates steam so the steam heat goes on as well; 2) While the circulator pump is working and the Zone 2 pipes get hot for the first 1 feet or so, it stops there so the hot water does not make it through the rest of the Zone 2 pipes.

I've tried bleeding the Zone 2 line, replacing the circulator pump, replacing the Pressuretrol, replacing the Aquastat, and replacing the thermostat. None of that did anything to address either problem. Does anyone have any idea what might be causing these weird issues? Thanks,



  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Something must be miswired with the aqua stat, so it can’t prevent the boiler temperature from going above the needs of the hot water loop. Do a search for that term here, and there are instructions for its installation.—NBC
  • Jamie Hall
    Jamie Hall Member Posts: 22,050
    Is the problem loop fed through a heat exchanger, or is it just trying to circulate boiler water? Water at 180 F will boil at only about 7 psi absolute. If the problem loop is being fed directly from the boiler, the pressure of the water at the second floor isn't much more than that even if the pipe is full of water -- so the water will happily boil as the poor circulator tries to pump it up there, and you will get no heat (no circulation).

    The steam comes on most likely because someone tried to fix the problem by setting the aquastat too high.

    Not much you can do about it except feed that second floor loop through a heat exchanger (a small indirect water heater could be used) and its own circulator -- and expansion tank.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 14,455

    You need a copy of @DanHolohan 's book "How Come" page 155 available here tells how to pipe a hot water loop off a steam boiler with and without a heat exchanger Sounds like a controls problem. Who wired the controls? Electrician, Plumber or Heating Technician?

    I would also check "find a contractor" on this site and post where you are located someone may have a recommendation

    A hot water loop off a steam boiler can work if done properly...don't give up you just need the right person.

    Don't throw the parts cannon at it that will just cost money and won't fix anything

    The first thing we need to know is does the hot water loop have a heat exchanger or is it piped off the steam boiler without one?

  • jneilan22
    jneilan22 Member Posts: 2
    Thanks for the feedback all.
    -- The Aquastat is set at 170 as the high limit.
    -- As far as I can tell, there is no heat exchanger on the system. The water feed directly from the boiler to the circulator pump, which then branches off to the 1st floor and 2nd floor.

    When the Zone 1 thermostat kicks on (1st floor), the boiler and circulator pump begin working, but no steam is generated through the steam zone heaters or pipes. Since Zone 1 and Zone 2 (hot water heaters) are both piped directly from the boiler and through the same circulator pump, does this suggest that there is something wrong with the wiring or would this be indicative of not having a heat exchanger?

    Thanks for all your help!

  • mattmia2
    mattmia2 Member Posts: 8,809
    @dopey27177 is sort of the expert on this, but anything above the boiler has to not have any vents on it and has to be airtight. If I recall the circulator has to have enough head to fill that loop with water because nothing else will.
    EBEBRATT-Ed Member Posts: 14,455

    Without an HX you can make it work on the 2d floor but it is a little tricky.

    You have to shut the boiler down and over fill the system with enough water to get up to the top of the 2d foor highest pipe. (about 1 psi for every 2' in height), then you have to get the air out of the hot water loop. When you drain the system down to normal the water stays in the HW pipes

    Think holding your finger on a straw filled with water