Bleeding radiators

Question

Some just Hiss no water, some hiss with water, some make no sound no water, is this normal?

One radiator staying cold after bleeding all as stated above several times? This radiator dies hiss air out , no water no heat. Any ideas?

Answer 1

On a circulating hot water system with bleedable radiators, if you open a bleeder and you don't get air+water or water alone, either the bleeder is clogged or the system pressure is too low to raise the water to that height above the boiler. Proper bleeding, after any air escapes, gives a solid stream of water with no spurts or bubbles remaining in it.

Check the pressure gauge on your boiler. For a 1-2 story house with boiler in the basement, the target pressure for a cold boiler is about 15 psi. If you have an automatic fill valve with pressure regulator and the mains supply is turned off, open the valve to allow the boiler to refill to the correct pressure. It should stop filling at around 15-18 psi. Close the valve if it goes higher and have the fill valve serviced.

Once you're up to 15 psi, bleed your radiators again. You should get air+water or water from all of them. If you do not, the bleeders are clogged and should be cleaned and replaced. (Beyond the scope of this answer.) And finally, refill the boiler after bleeding.

If the pressure was low and it takes only a tiny amount of water to bring the pressure up, your boiler's expansion tank is shot; time for a new one. Another sign of a failed boiler expansion tank is if you bring the boiler up to pressure then turn off the water supply valve, but bleeding a radiator yields only a little water and you see a marked pressure drop.

If you don't have a working pressure gauge on the boiler, you need a service call.