Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Boiler feed tank overfills

A customer has a job where he installed a Burnham V9A commercial boiler. He has 3 large motorized valves on the. There is a boiler feed pump (49 gallon) controlled by a McDonnell and Miller 150 pump control. The system is operated by a Vapor stat . Cut in is 4oz and out at 16 oz. After about 3-4 days usage the system overflows from the tanks vent pipe. This has been happening for 2-3 months since the boiler was installed. The customer thought it was the 150 pump control and that was not the case. I thought it might be a dirty boiler causing this and have instructed the contractor to clean this well. Any other thoughts


  • Jamie Hall
    Jamie Hall Member Posts: 23,428
    This is probably a really dumb question -- but what controls the level in the feed tank? It may be that the combination of the motorized zone valves is such that condensate may be held back in the returns -- not much, but some -- and whatever is controlling the level in the feed tank senses a low water condition and adds water when there is still condensate held in the system. Vacuum breakers on the returns/mains after the zone valves?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 15,613
    3 things.
    The boiler feed tank may be undersized. The make up water to the boiler feed tank could be leaking by. Make up water to the boiler could be leaking by (if you have that).

    Also what @Jamie Hall mentioned above
  • dopey27177
    dopey27177 Member Posts: 887
    1.The float control on the feed tank may need to be adjusted.
    2.The check valve on the pump discharge may be leaking allowing boiler water to reenter the condensate fill tank
    3. do all zone valves open at the same time, if so the amount of steam leaving the boiler could be causing excess water to be retained in the system
    4. find a way to stagger the opening of the zone valves.

  • dopey27177
    dopey27177 Member Posts: 887
    PS Check to see if there is a leak in the fill valve to the boiler feed pump set.
  • retiredguy
    retiredguy Member Posts: 914
    What is the model number and pipe size of the motorized zone valves? How long does it take for each of the zone valves to open? What is the boilers input? Is this a whole new job or did the new boiler replace an existing boiler. If there was an existing boiler do you have any specs on the old boiler, type, size etc. When the boiler fires does the water line in the gauge glass remain stable or does it fluctuate (bounce up and down)? also @Jamie asked but what controls the level in the feed tank? And @EBEBRATT-Ed and @dopey27177 both asked good questions. There are a lot of possible fixes, but more system information is needed. Add a few pictures if you can.
  • New England SteamWorks
    New England SteamWorks Member Posts: 1,518
    Is there a PRV on the domestic water inlet?
    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems