Occasionally radiators do not produce enough heat or they don’t radiate any heat at all. The most common reason is that the radiator is not full of water and has air in it, preventing the continual flow of hot water from the boiler. This is the first thing to try if some radiators are warm and one or more are not. The vast majority of older homes have cast iron radiators with individual bleeder valves. This process applies to these homes. Obtain a radiator bleeder key from the hardware store, the best ones have two options; a blade like a screw driver and also a square hole.
1) Open the vent (bleeder) at each radiator to see if water comes out. Have a rag (any small cloth) in the other hand to catch the water.
2) If air comes out, and there is pressure, keep it open until water comes out or there is no more hissing of air.
3) If there is no water coming out, add water to the system keeping the pressure no greater than 20 psi. DO NOT EXCEED THIS PRESSURE. Repeat the first two steps.
4) Repeat the above steps for all radiators in the house. Air may collect in individual radiators. The presence of air and the location of that radiator is irrelevant to knowing the condition of the other radiators in the building. It can save time to start with the upper most radiators and work your way down.
If you do not know how to add water to the boiler or are not comfortable with this process, give me a call and I can stop by and show you how to do it on your boiler. If there is no more air in the radiator(s) and it(they) is(are) producing little or no heat there is something else wrong with your system.
If you have small baseboard radiators with a thin metal covers AND pipes at the boiler each with individual drain valves, the process for getting the air out is NOT THE SAME. I would strongly suggest calling a professional to work on this type of system.