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.

Differential Bypass

Nron_13 Member Posts: 164
no bypass valve will shut off 100% they will all leak pressure past add an isolation valve if you need to


  • Steve_56
    Steve_56 Member Posts: 15
    Differential Bypass

    I'm retrofitting my house and this is my first experience with a differential bypass.

    I have a secondary mixed loop with a varying load, so I installed a 3/4" Honeywell diff bypass. Says its adjustable up to 17 psi. Anyway, while playing around with things, I dialed up the bypass all the way to try and eliminate any flow through it. But it seemed to still allow some water through. To test the theory, I turned off all the pumps (system static pressure is 12 psi right now), opened up the valve, and water started coming out!

    After disassembling the valve, I found that the water is leaking through the pressure readout chamber. This chamber has supply water on one side, return on the other, and is spring loaded so that the differential reads out on a gauge. The only problem is, the sliding portion isn't a tight fit or even gasketed (just a plastic piece), and allows water through.

    I assume this is by design and some diff bypass have a little leakage which is negligible in comparison with overall system flow? I just didn't see any info on the (one page) manual that mentioned the leakage, so I didn't know how to characterize it.


This discussion has been closed.