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what might be the cause for one radiator not get heat ?

Hi folks !

Happy hloidays & the best for 2010 , my situation is with one radiator in a bedroom that's not getting any heat, after bleeding 9/20 from this hydronic heating system the first level is giving good heat , but the problem is mainly this room that has two radiators one larger than the other one which is preety much smaller, meanwhile the attic radiator which is preety big ,gives alot of heat where no one really occupies this area only maybe to relax :p I really don't know what to do ,does anyone think that bleeding all the radiators will make any difference? :confused:

Re: what might be the cause for one radiator not get heat ?

That one Radiator may have air, try bleeding it and see if that works, Nashuatech will be along at some time to lend you his expertise, he is the man. Good Luck!!! :)

Re: what might be the cause for one radiator not get heat ?


I agree with Sten---try bleeding the cold rad if you haven't done so already to see if that makes a difference---if not, the problem is probably related to a FLOW PROBLEM, instead of an AIR PROBLEM.

A balky HW radiator can be a tough nut to crack----there's about 10 different things that could go wrong: the under-floor piping may have air-catching loops that inhibit good flow; there may be crud accumulated in the piping inhibiting good flow; there may be an AIR POCKET between the HW supply & the riser to the radiator; etc.,etc.,etc.

The hopeful news is that most balky rads can be brought back to normal heat in time.

Consult the sites below to learn from expert Dan Holohan about the different piping arrangements that are installed in residential heating systems---Holohan makes the argument that it is almost always a FLOW PROBLEM that stops a radiator---he compares HW flowing thru a pipe to a rad to cars on a freeway---if cars hit a traffic jam on the freeway during rush hour---THEY TAKE THE PATH OF LEAST RESISTANCE---and take an alternate road if one is available.

Hot Water flowing thru a pipe does the same thing---it always follows the path of least resistance.

So, if your dead rad is fed hot water by a diverter loop or diverter-tee (also called monoflo tee)(common in these setups), if the water "sees" any resistance (crud,air pocket) in its intended path thru the radiator, it will STAY IN THE MAIN SUPPLY PIPE (least resistance) & not go thru the radiator at all---you'll have to study the pipe-flow diagrams that Holohan has & see if you can inspect your piping system to determine if you have a one-pipe diverter loop (most common)---if you have an on/off valve on each of your rads, you probably have such a diverter loop, as noted in the diagram.

Please post back if you have on/off valves on your radiators, & make sure they are completely open.

For the articles by Holohan, you'll have to Google "diverter-tee-hot-water-heating" and "loop-hot-water-heating" to get the articles that have the piping arrangement that you have (diverter-tee) if you have on/off valves on your rads.

You will note on the "high performance" site, that one can install an on/off valve only on the diverter-tee (monoflo tee) or two-pipe piping arrangements---unfortunately, it is precisely THESE piping arrangements that allow an alternate path for the hot water to bypass the radiator & flow thru the main supply pipe.


I have the same problem

For some reason, some radiators on the first floor heat better than others on the first floor.

Some radiators on the second floot heat better than other radiators on the second floor.

The radiator in the attic had new copper pipes installed some years ago. the pipes I can see and feel from the second floor bathroom. The pipes are hot, but the radiator is only luke warm bottom half and stome cold top half.

I will try bleeding this pipes, and get back with resuts.

Is this problem becasue my boiler has a 18 psi and is at 112 degrees?

Re: what might be the cause for one radiator not get heat ?


The reading of 18 psi sounds ok, but the temp reading of 112 degrees is WAY TOO LOW---radiators are designed to operate at 180 degrees---I don't know why your water temp is set this low, but is often done in radiant heat setups.

Sometimes 112 degrees is used to temporarily lower the water temp to maintain more weight to the flowing water (very hot water is much lighter)---this sometimes enables the water to flow thru higher up rads & the temp is then raised once good flow is established.

The upstairs & particularly the attic rads may be so high from the boiler that the water at 18 psi does not have enough pressure to get to the attic rad.

Another possibility is that your current circulator (pump) doesn't have sufficient head to push water thru the upper rads.

You can calculate if you have enough psi to get the water to the attic rad by the formula:

height (ft.) = 2.31 X psi

Thus the vertical height the water will rise from the boiler in the basement is 2.31 feet for every 1 psi of water pressure.

Thus 2.31 ft. X 18 psi = 41.58 feet.

Thus if your attic rad is above 41.58 feet in height from the boiler, the water won't get up to the rad unless the boiler pressure is raised by adjusting the pressure reducing valve slightly higher.

But before adjusting the reducing valve, raise the water temp in the aquastat---standard settings are 160 degrees for low limit and 180 degrees for high limit.

Post back if you don't know how to do this.

Also open the bleed valve on the attic rad to see if you get water----if there is a healthy flow of water from the bleed valve, you have sufficient pressure & the answer to no heat is to be found elsewhere.

You can actually measure the height of the distance from the boiler to the attic rad to see if it exceeds 41.58 feet.

Also study the piping article by Holohan at the sites listed in the previous entry---if you have shut'off valves on your rads, that means there are 2 ways for the water to flow thru the pipes to the rad-----also note, if you have shut off valves on your rads, make sure they are turned counter-clockwise 180 degrees (half circle), all the way open---many on/off valves have a little brass stop on the underside that gets snapped off & the valve is allowed to turn 360 degrees (full circle), instead of the intended 180 degrees---this ACTUALLY CLOSES the valve again, so take a mirror & flashlight & make sure the metal stop (tab) hasn't been damaged---if there is no heat from the lower rads, as you state, try turning the on/off valve 180 degrees counter-clockwise to make sure it is open & test for heat again.

If these steps don't do it, post back, there are other things you can try.

Re: what might be the cause for one radiator not get heat ?

Hi NashuaTech,

I had to go out and buy a bleeder key. Could not fine one in the house and the previous owner said that she did not remember ever seeing one. She said that the company that she called annually to check the the boiler took care of that.

OK, so I did bleed the radiator on the first floor summer kitchen, main bedroom radiator on the second floor and the attic radiator.

The first floor and second floor radiators did nto ahve any air. Water came out right away. But stil, they feel lukewarm.

The attic radiator did have a lot of air. Took several minutes for the air to empty out, but then water to start come out. After several hours, the attic radiator started to feel warm. It will take more time for the attic to feel the heat.

I am not all that familair with my hot water boiler system. But hours after I bleed my attic radiator, the psi is now at 20 and the temp is now at 120 degrees. I do not know how to adjust these settings. It is a Weil-McClain boiler and the pump is for pumping the hot water, after the radiator has warmed it up. Without my adjusting anything, these numbers changed. I wish these things came with manuals.

I will take pictures of my boiler system and post them here next time.

I do not understand why the main bedroom and the summer kitchen is only warm and not hotter. The main bedroom is farthest from the boiler (after the attic) and the summer kitchen is above and just feet away from the radiator. However, the summer kitchen is over a crawlspace, not the actual basement. I shiver at the thought of going into the crawlspace, but I guess I have to do it. I'm thinking maybe I should just wait until the Spring, to get into the crawlspace.

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