I recently bought a newly remodeled 1950's era house about two months ago. It has a Weil Mclain fuel oil boiler that provides heat to four different zones (loops) in the house. Each zone has a couple of new baseboard radiators (the style that mount to the wall and run the whole distance of the wall). The system works well, except for the zone that covers the master bedroom, which pings very loudly.

In the past with similar systems there has been a bleed valve by each baseboard radiator. However, there are no bleed valves on any of the radiators. Is there another common style of heating system with bleed valves in other locations? Or is there another mechanism of bleeding the individual zones that I'm missing?

1 Answer 1


Other than looking for hidden bleeders (i.e. I have one where the baseboard cover needs to be removed to reveal the bleeder) and bleeding any bleeders that you can find, you may need to swear at whoever put in the new radiators and retrofit bleeders where they are missing.

There is often an automatic bleeder/vent on or just after (in which case it's often on a big cast iron "air separator" that may have an expansion tank hung off its bottom) the boiler, since in theory any dissolved air will be most prone to come out of solution where it's hottest - if that becomes clogged or otherwise inoperable (they don't last overly long) air may migrate elsewhere more than it would if that was working. Sometimes people see a dribble from these and close down the cap on the "tire fill valve" rather than replacing them - which renders them inoperable. I think it's bad practice to depend on that for bleeding the whole system.

Given how anemic circulator pumps are when faced with air bubbles, the only other way of getting that loop clear would be to open the boiler fill and open a drain on that loop, so that the fill water can push the bubble through to the drain - but then you have new water in the system, and some air will come out of that.

  • I took off all the radiator covers in the house and I found a single bleeder valve hiding in the upstairs bathroom behind the toilet. To bleed all four zones it seems like I'd need to turn up all the zones at the same time to circulate the water and then bleed that single radiator and that should work for the entire house. Does this sound correct?
    – Pridkett
    Jan 12, 2014 at 3:27
  • 1
    If that is the high point of the system, most air may already be accumulated there; if you bleed out what is there, let the system operate for a while, and bleed again in a few hours or a day, you may get it all. You don't particularly need all the circulators running as you bleed.
    – Ecnerwal
    Jan 12, 2014 at 15:13
  • @Pridkett did that work out?
    – benji
    Mar 18, 2019 at 19:32

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