Hot water boiler won't fill radiators

Old 12-20-18, 03:22 PM
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Hot water boiler won't fill radiators

hot water boiler doesn't fill radiators, even the expansions tank is empty. Changed the bearing assembly in the circulator pump, water is running but don't know where it is going. The pipes above the boiler get hot but the water doesn't reach the radiator. very old boiler, NRC, series 3
Old 12-20-18, 03:39 PM
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Going to need a lot more info and pics of the boiler and at least the near boiler piping if possible.

When you say expansion tank, is it an extrol or conventional steel tank up in the ceiling. Bearing assembly has nothing to do with pressurizing the boiler unless you just mentioned it because you had to drain the boiler to change it.

If you can hear water running it must be going somewhere. Start feeling pipes to see which ones are cold and is there any reading on the pressure gauge.

Pics would definitely help.
Old 12-21-18, 05:12 AM
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First thing to do is go to one of the cold radiators, open the bleed valve at the top of the radiator using a vent key or screw driver and see if air, water or nothing is expelled. If it is air, you need to vent all the air from the system. If it is water and the water is cold you have a circulation problem. If nothing comes out, or first air then nothing, you need to add water to raise the pressure in the system. To find the cold fill minimum pressure you need (if you are interested), , measure from the highest point in the heating system down to the pressure gauge and multiply that footage by .433. then add about 2 psig to that figure. Vent the top floor rads until water comes out the vent. If you don't want to do the measure idea, boiler guys from my era usually set the system make-up PRV to 12 psi for a 1 story home, 15 psi for a 2 story home, and20 psi for a 3 story home. If you can add a picture of this boiler. I haven't seen one of these nfor years.

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