Radiator furthest from boiler output not hot

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Old 02-20-12, 08:12 AM
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Radiator furthest from boiler output not hot

I have a oil-fired, hot water Burnham boiler, works great, except the radiator furthest from the boiler output (on the 2nd floor, opposite end of house) rarely gets warm. I'd say 9x out of 10 its ice cold.

What can I do? Thanks in advance.
 
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Old 02-20-12, 09:37 AM
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How are the radiators piped? In series? With parallel supply and return lines? A monoflo system with each radiator piped off a single main header, serving as both supply and return? Just one zone (i.e., just one thermostat)?

Has this problem always existed? What does your boiler temp gauge read?

Photos of your system would help.
 
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Old 02-20-12, 10:01 AM
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I don't know about the first few questions, but it is one zone. Each radiator does have two lines on either end, I am assuming one is supply and one is return. Home is 1940s.

Problem has always existed. I'll have to check the temp when I'm home. I will also post pics.
 
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Old 02-20-12, 11:12 AM
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Are these large cast iron radiators?
 
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Old 02-20-12, 11:33 AM
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Old 02-20-12, 11:41 AM
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When you get home, go to the boiler and read the pressure gauge. You should have a min of 12 psi when the system is cool. If the pressure is ok, bleed the radiator of air via the vent at the top.
 
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Old 02-20-12, 11:45 AM
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How should I bump up the PSI if that is the case?
 
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Old 02-20-12, 01:13 PM
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OK, but we need to see how the radiators are piped. Take photos from the basement. Also, wide-angle photos of the boiler and surrounding piping.
 
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Old 02-20-12, 02:14 PM
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Modern systems have an auto-fill valve that will maintain the pressure in the boiler system. If you have one and your pressure is low, it could mean the auto-fill valve is defective or there is a shut off valve that is closed.

I don't think the piping strategy matters now that we know it is cast iron radiators. Any air in the pipes will collect at the top of the rad.
 
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Old 02-20-12, 02:17 PM
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I would say that the first thing to do is try and bleed the rads of the air... and go from there is that don't work.
 
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Old 02-21-12, 09:16 AM
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This picture



shows that the installer wasn't all that bright. The automatic air vent is flat out wrong and the "loop" (down and up) piping to the expansion tank is even more wrong. That auto air vent needs to be removed and the piping from the expansion tank installed there with a smooth upward rise to the tank.

That may not be cause of your current problem but it IS a problem.
 
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Old 02-21-12, 10:22 AM
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Which one is the auto air vent? And why has this issue not been brought up by the HVAC company when they come for the annual check-up? And how is it possible for the unit to be running at 91% efficiency (according to the tech)?
 
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Old 02-21-12, 01:03 PM
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The auto air vent is the little can with the tire valve cap at the top of the vertical pipe on the far left side of the picture. Using auto air vents in a system with a "conventional" expansion tank (the tank in the upper foreground of the picture) causes the air in the system to be expelled rather than diverted to the expansion tank. The net result is a lowering of the pressure in the system.

That lowering of pressure in turn will cause the auto "make up" valve (also called a PRV, or Pressure Reducing Valve), the red item in the center of this picture



to add more water to the system in order to raise the pressure. Eventually the expansion tank becomes "waterlogged" and cannot absorb the pressure fluctuations between cold and maximum temperature and then the safety valve on the boiler (which I don't see in any of your pictures) will "lift" at the higher pressures and blow water out of the system which then causes the cycle to increase and causes all sorts of problems.

As for why no one has made a point of this improper piping, most likely because they (1) don't realize how improper it is, and (2) they drain the expansion tank every year and forestall the occurrence of the problems I described.

I can also assure you that your system is NOT running at 91% efficiency. The ONLY "efficiency test" commonly done is a combustion efficiency test and that is but one part of the overall system efficiency. Further, that boiler/burner combination is incapable of achieving more than maybe 85% combustion efficiency on the best of days. If your technician is getting 91% efficiency ratings then he (she) is not performing the testing correctly.


Now, lets see a few close-up pictures of where the radiators connect to the main piping.
 
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Old 02-21-12, 01:26 PM
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Thanks so much for the feedback, Furd. What do you recommend is a good first step in getting things sorted out properly?
 
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