I have trouble bleeding out attic radiators. Residential hot water + gas system with boiler, bladder tank and auto-fill all in the basement, rads on 1st, 2nd, 3rd floors. All rads on 1st and 2nd floors bleed easily and auto-fill does its job.
On third floor, I get a little air wheezing out then it stops. I have to run up and down, open the valve so it fills up to 29 pounds, then let a bit more air out til it stops, and so on ..... a dozen times til I get water out of the radiators in the attic. What's more, this ONLY works if I call for upstairs heat. Without that I get nothing .. the rads won't bleed out even at 29psi.
I don't think the standard 12psi of an autofill is enough to fill the third floor ... I think the top of the highest rad is about 27' above the boiler. But when I fill it up to 29psi, it bleeds down to 18, then stops. Maybe the meter is inaccurate. Can anyone help me understand this, and more puzzling, why calling for heat helps? Is it opening the zone valves that helps? It shouldn't ... pressure acts on the return too. It the circulator helping? It shouldn't ... it's tiny, it's not a pump.
On third floor, I get a little air wheezing out then it stops. I have to run up and down, open the valve so it fills up to 29 pounds, then let a bit more air out til it stops, and so on ..... a dozen times til I get water out of the radiators in the attic. What's more, this ONLY works if I call for upstairs heat. Without that I get nothing .. the rads won't bleed out even at 29psi.
I don't think the standard 12psi of an autofill is enough to fill the third floor ... I think the top of the highest rad is about 27' above the boiler. But when I fill it up to 29psi, it bleeds down to 18, then stops. Maybe the meter is inaccurate. Can anyone help me understand this, and more puzzling, why calling for heat helps? Is it opening the zone valves that helps? It shouldn't ... pressure acts on the return too. It the circulator helping? It shouldn't ... it's tiny, it's not a pump.