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.

Flow Check Valve: yes/no?

TAG Member Posts: 755
I have not installed a new system is a few years .... looking and reading many threads -- don't see any flow check valves? The Cast iron Type. I was always told the circulators did not restrict fantom flow. What's up?

It also seems that purchasing the circulators with internal flow checks is the norm .. I'm not seeing how they are necessary -- and they don't stop unwanted flow?

What am I missing?

I would think the check valve in the circulator must cause some restriction.


  • mikeg2015
    mikeg2015 Member Posts: 1,194
    I’ve found that I get some phantom reverse flow on my indirect I installed recently despite the check valve and circulator facing vertically. Not sure if its leaking by just a little, probably due to normal surging/pulsing and differential from the boiler and the condensate return where the indirect connects to.

    Temp gauge on the supply will show 140F, while return shows 200F so some heat is clearly backing up. I’ll eventually add a flow check on the 1/2” bypass and return line here eventually.

    Not super critical since I have a mixing valve on the indirect output. Probably getting 2-3k BTUs of heating on the tank when the boiler is steaming.

    First install of a steam boiler and indirect for me, so live and learn. Also need to put a valve on the strainer ot blow it down at least once a month with boiler rust scale (it’s a used boiler... won’t do that again either).
    HVACNUT Member Posts: 5,863
    It's been more than a couple years for you. Internal flow checks have been the norm for quite a while now. They pop out very easily if you want to use a different method.
  • Intplm.
    Intplm. Member Posts: 2,000
    They do not cause a restriction. At least not a restriction that would affect "performance".
    Phantom flow isn't really a phantom. It's part of thermodynamic law. "Hot goes to cold always."
    So in the summertime when you have a boiler that runs to maintain temperature and/or to make domestic hot water, the cooled radiators will have some of that hot boiler water go up into a cooled radiator partially heating that rad.. This is what flow control valves are meant to prevent. .......the hot going to the cold.
  • TAG
    TAG Member Posts: 755
    It's been a while since I did a whole new system -- all of my systems have used high mass cast iron Buderus boilers. It's not that I have not seen the small pumps w/ the check valves .. just went with what I have used in the past.

    This new build is going to be a wall hung and radiant ... no high temp panels or high mass radiators. I'm also using LLH's -- all new to me. The house .. I'm having installed. My new 1700sf studio ...I'm going to be doing myself.

    Anybody use the B&G check-trol -- this has the flow control in the valve flange.
  • mattmia2
    mattmia2 Member Posts: 9,741
    One nice thing about the separate flow check is that you can get versions with a manual bypass control.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    My personal experience with the IFC's is that they make noise, kind of a rattling sound when the circ is running. If that will be a concern, I remove it and install a typical weighted check. I like the bronze swet-check as they end up being cheaper than an iron one and a male adapter(s) for copper. And they are quiet, but do have a significant equivalent length of pipe.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!