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Hissing vent troubleshooting

David Nadle
David Nadle Member Posts: 624
Two of my rad vents are hissing loud and long after they should have closed. It's happening in the morning coming out of setback so everything's pretty cold. This is a new boiler, installed last month. All rads have brand new Dole 1As. Here's what I know:

- The boiler was not skimmed or cleaned for about a month after install and was used moderately during that time. The waterline had been pretty bouncy before that.
- I'm halfway done insulating the mains. I read where that sometimes create a vacuum but I don't think that's what's happening.
- The pressuretrol is set at 0.5 with 1.5 differential. As far as I can tell it is not cutting out in the morning, probably because these two vents aren't closing. They just hiss until the thermostat is satisfied.
- I haven't checked the pitch of the rads yet but they were perfectly quiet last year.

Is it possible the month of dirt/oil in the water wrecked these two brand new vents? I'll gladly get some new ones if I'm overlooking something that will ruin every vent I install I'd like to know.

Love to read your thoughts.


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