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Radiator not heating

I have oil hot water heating and I have cast iron baseboard heaters in my living room that will not heat up. All the other radiators in the two story house heat up very well. I tried bleeding them several times and I get a little heat in the first radiator in the room but I get nothing in the second one. The bad part about this is the thermostat is in the living room so the furnace is running more than it should because it thinks it is colder than it really is.

The heating is all on one zone...Any ideas?

Re: Radiator not heating


You have a boiler there, not a furnace.

From your post it sounds like the non-functioning rads are on the 1st floor.

Is this true, & have you tried checking to make sure the on/off valve is turned all the way to the left on these rads.

The on/off valve should move no more than 3-4" counterclockwise to open the rad then stop; if the handle keeps turning, the little brass valve stop under the handle is probably snapped off; you can actually turn the rad off again if the on/off valve handle is defective.

Aside from the on/off valve being partially closed, another major cause of cold rads is air in the top of the rad; since you have already bled the rads, it seems to be something else.

A third cause could be a blockage at the base of the rad due to an accumulation of iron oxide sludge; this is a black, gooey sludge that looks like used motor oil & collects at the base of the rad & can block the in-pipe & out-pipe to the rad.

This will cause especially a diverter-tee piping arrangement to have the hot water bypass the rad due to higher resistance because of the sludge.

Other no-flow causes could be a diverter valve installed improperly, long or small diameter risers, etc.

Also if you don't know the particular piping arrangement you have on your system, check at the sites below to see if you have a "series loop" arrangement, a "diverter valve" piping arrangement, or a "2-pipe" piping arrangement.

Scroll down & click onto the headings to view diagrams of the different piping arrangements.

If you have on/off valves on each rad, you probably have one of the latter three piping arrangements.

Generally, a "series loop" piping arrangement is set up so that the pumped water from the boiler goes thru one rad, then directly thru the 2nd rad, then thru the 3rd rad, etc. this type of arrangement often makes for uneven heat, but it won't result in one or two rads not heating; if there is a blockage with this piping arrangement in any part of the piping, none of the rads will heat up.

As the diagrams show, other systems allow the hot water to stay in the "main piping" if there is a restriction in the rad, & thus, this piping arrangement CAN cause one or two rads to go cold.

Please post back to advise a) what piping arrangement you have; b) that the cold rads are on the 1st floor; c) that there is little or no air in the rads; and also, that you get water coming out of the bleed valves after the air is expelled.

If you bleed one of the cold rads & NOTHING comes out, please advise.

Does air keep getting back into the system even though you bleeed it regularly??


Re: Radiator not heating

I have a diverter tee hot water system. On the radiators in the living room(cast iron baseboard)there are no shut off valves. When I "bleed" them all I get is water, never get any air out. i can bleed out 2 gallon and no air. Oh, and you are correct, these are on the first floor.

Re: Radiator not heating


The strategy applied to a situation like this is to use less invasive methods first, then graduade to more invasive surgery, if necessary.

In order to get flow back in the rads, pick a warm or mild day, & shut off the boiler switch & shut off the water inlet valve at the boiler so no additional water is allowed into the boiler piping; allow the boiler water to cool off for 1/2 hour or so.

Get a large bucket & take a wrench & remove the bleed valve so a gallon or two flows into the bucket.

It's a good idea to have a spare bleed valve handy; they are available at HD/Lowes & are of universal fit.

Have the bucket ready to catch the water, because it will spurt out for a minute or two.

Quickly retrieve the bleed valve if it falls into the bucket; if the water quickly fills the bucket, simply put your finger over the bleed valve hole in the rad to stop the flow.

Temporarily replace the bleed valve, & empty the bucket, & carry on removing a few gallons of water from the rad until the water stops flowing.

When the water has stopped flowing, clamp a bicycle tire valve onto a bicycle pump & insert the rubber end into the rad hole.

If this is a tight fit, excellent; if it's not try an auto tire valve whittled down with a utility knife.

Pump about 10 strokes with the pump to inject some air into the rad to try & open up the passages; you may need a helper to hold the tire valve steady in the bleed valve hole.

Repeat this process several times & then replace the bleed valve back in its hole & tighten.

Reopen the inlet valve at the boiler & allow the system to replenish the lost water.

Bleed the rads on all floors & turn on the boiler switch when the gauge reads at least 10 psi.

I would try this method first, since it doesn't involve taking any piping apart, or soldering, etc.

If it doesn't work the first time, it may very well work the 2nd time; so try it twice.

An alternative method is to turn off the boiler, open the bleed valves on the top floor, & bleed the system thru the boiler drain valve.

Post back when you have some results.

Also check the diverter valve or valves on the piping branch that goes to the cold rads; they are also known as monoflo tees or venturi valves.

They usually have an arrow stamped on them indicating the correct direction of flow (supply or return).

If the diverter valve is positioned on the supply riser end of the rad or rads, the arrow should be pointing in the direction of the water flow in the main pipe supply; if the DV is positioned on the return riser end of the cold rads, the return arrow should be pointing in the direction of main pipe water flow.

It's quite common to see these valves installed backwards, & thus is a major reason for cold rads with this type of piping system.

These valves work because of their internal construction, which "scoops" 1/2 the water flowing in the main pipe & "diverts" it to flow thru the rad; when a monoflo tee is installed on the return leg of the rad, the monoflo tee "sucks" a certain portion of water thru the rad; these scooping & sucking actions create a path of resistance that favors water flow thru the rad, instead of the water staying in the main (water flow always follows the LEAST PATH OF RESISTANCE).

The main reason for cold rads is that the water flow thru the main pipe usually encounters less resistance, so it stays in the main pipe, & bypasses the rad; excessive resistance in the rad, in turn, due to dirt, etc., creates too much of a restriction for good water flow thru the rad.

Bell Gossett has literature on these valves at the site below; click onto "Homeowners", then scroll down & click onto "valves" then onto "Monoflo fittings" (B&G uses a "red ring" on the valve to designate how the valve should be installed; other mfgs use "supply"/"return", as noted).

Check out the literature list at the site to see diagrams of how these valves work; often two monoflos are installed in cases where the rads are chronically cold, one at the supply riser & one a the return riser.


Re: Radiator not heating

I am thinking of builing a new home crsftsman one story. But there is afew things I need help with, Such as heating an air hot water insulation and other grren products. I guess my question is, how much is there a differnt is radiatiant heat compared to forced air. and how can I have air with radiatiant heat...thanks dan

Re: Radiator not heating


Your question on HVAC options for your planned house is a good one.

However, I wonder if you could post it as a separate listing so everyone has a chance to see the content of your post.

This will assure that you get a wide number of replies.

To start a new thread with your own title, Click onto the bright red "NEW THREAD" icon at the very bottom of the Heating/HVAC section.

Thank you.

Re: Radiator not heating

in cases like this my motto is keep bleeding. if all else fails bleed out a ton of water. some times you may find a hidden air pocket futher down the line than you expected.


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