I have three heating zones (forced hot water in baseboards) in my house. On the top floor, one zone controls all the baseboard heaters on that floor. None of the baseboards on one side of the house in that zone work, while the baseboards on the other three walls does work. None of the baseboards on the non-working side have bleeder-valves that I can find. I have tried bleeding the entire system from the boiler, but still those baseboards do not throw any heat. Any ideas on the cause and possible solutions? Thanks!

  • air lock maybe, what happens when you turn off all working heaters? Commented Mar 9, 2014 at 23:44
  • If this is the system type I have, there is no "turning off" a section of baseboard (other than closing the flaps on the cover) - when the circulator runs, all the baseboard gets water, with no additional valving, unless there's a balancing valve for the loop, or one circulator and several zone valves.
    – Ecnerwal
    Commented Mar 10, 2014 at 3:44
  • Correct, I cannot turn off a section. It's all or nothing.
    – tony
    Commented Mar 10, 2014 at 15:04

1 Answer 1


It sounds like the second floor system is split (one zone, but not a single loop of pipe) so that water is circulating in half (or three-quarters), and not in the other half (or quarter).

You either need to look harder (pull the covers off if you have typical fin-tube baseboard) for bleeder valves you are not finding, or cut the system open and add some. You have classic symptoms of air in the system, and there should be bleeders at the high points of the system, since you really can't get all the air out by bleeding down in the basement. If you have any bleeders on the working sections, certainly give them a try to see if there's any trapped air there, even though they are working.

The small-percentages possibility other than that is that the system has actually frozen on that side. Air-lock is far more likely.

  • This is probably a stupid question, but would the bleeder be obscured by the fins? I checked the exposed sections of pipe not covered by fins, but not within the finned sections. Maybe that was my mistake.
    – tony
    Commented Mar 10, 2014 at 15:02
  • No, they are normally located on elbows where the pipe comes up through the floor (or on one of my runs, where the pipe doubles back on top of itself) - they won't be in-between the actual fins. They are often hidden by the end-caps of the covers.
    – Ecnerwal
    Commented Mar 10, 2014 at 15:38

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