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.

hissing radiators

good evening. i was on a job to day (not a heating job) and i noticed that every radiator air vent was hissing. the radiators are all one pipe baseboard(except for one). the mains both have brand new Hoffman 75's which i put in a few weeks ago. the pressurestrol pigtail was mounted on the McDonnell 67 lwco and was set for .5 psi cut in and a differential of 1. the 0-30 pressure gauge was mounted on the same pigtail and was going up to 3 shutting off dropping to 1 in about one minute and then going back on. there was a small leak where the L shaped copper tube connects to the lwco. i wonder if this can contribute to the rapid pressure drop. to make a long story short why is the pressure dropping so fast and why are the vents hissing. any ideas would be greatly appreciated.

p.s. the tapping coming out of the boiler was reduced and then increased again where the riser connected with the header


  • nicholas bonham-carter
    hissing vents

    most likely the pressure is too high, combined with bad main venting. if the pressuretrol is piped to the LWCO, it can pick up a lot off debris which collects in the LWCO, and get clogged up, and unable to perform its job, raising the pressure beyond the few ounces necessary for it to work properly.

    probably the short-cycling, and the leak, is a result of inadequate main venting, and the over-pressure.

    check the mfg's piping instructions to see if they have specified a funky reducer/increaser for the riser!!--nbc
    STEAM DOCTOR Member Posts: 2,012

    there are two 2" mains   about 20' long each. both are vented with new Hoffman 75's. i blew through the pigtail and it was clean. the LWCO is a few weeks old so it should not have much buildup.
This discussion has been closed.