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Cold Radiator

I have a one pipe hot water radiator system. All the raditors work, except for a baseboard one in the kitchen. I have bled the radiator and did not find any air. I was wondering if the turn valve needs to be replaced and if this could be the problem? Any other thoughts of what might be creating this problem. Also, if I need to replace the hand valve how do I do it?

Re: Cold Radiator

Ah yes, the perennial hot water system cold radiator problem.

Please provide more info as to what type of piping system you have.

You state you have a "single pipe" system, but this could mean a) a series loop system where the main supply from the boiler goes into one rad, then thru the next, etc.,etc.

Or b) a single pipe diverter valve (also known as monoflow tee or venturi tee system) where diverter tees on the "one pipe" divert part of the water thru each of the rads in turn.

The different piping systems are illustrated in the diagrams on the website below.

Click onto loop piping system and diveter valve system to determine which type of system you have.

Also look at the piping and valve arrangements in your cellar to clarify this.

Read the commentary on hot water piping at the heating help site to get an understanding of how hot water flows in a heating system (always follows the least path of resistance).

Diverter tees usually have a large arrow stamped on the brass valve, or the words "supply" or "return".

How long is the baseboard section that covers the kitchen???

If it is over 15', it may be so long that the weight of the cold water sitting in it is causing the hot water in the "one pipe main" to BYPASS the kitchen baseboard and go right back to the boiler.(this would hold true if you have a diverter-tee one pipe heating system).

Another cause of the cold baseboard, as you noted, may be that the on-off valve has failed.

Get all the way down on the floor with a strong light and turn the valve in both directions.

Many of these valves have a small vertical brass stop that stops the travel of the valve between the ON and OFF positions.

If the valve turns freely, chances are it is ok.

When you opened the bleed valve, did you get water coming out???

If you got nothing, there's no water getting into the baseboard.

If you get water when the bleed valve is opened. get a large bucket and allow a gallon to bleed out.

Go down to the boiler & make sure the automatic fill valve is replenishing the gallon you take out; the gauge should read at least 12 psi.

Sometimes some gunk can clog up the rad, especially if you have hard water in your area.

If you get nothing but clear water, then the problem isn't an air bubble that making the baseboard cold, it's a FLOW PROBLEM.

The bleed valve is usually on the opposite side from the on/off valve; if you get a lot of water out of the bleed valve, it means the on/off valve is working, and you've got a FLOW PROBLEM.

A FLOW PROBLEM can be caused by a length of baseboard being too long (over 20') or only one diverter valve on a monoflow system, or gunk in the baseboard, if you have hard water in your area.

Other remedies may involve removing the on/off valve altogether, installing another diverter valve (if this is the system you have), or closing down the system, removing a gallon or so from the boiler to remove the on/off valve.

Can you solder copper pipe, and is this what you have for the connections at the baseboard???
Please post back.


Re: Cold Radiator

I have a diverter tree system. I have two zones- the basement (on it's own thermostat) and the main floor and upstairs controlled by one thermostat. The radiator that is cold is on the main floor. I am not sure as to the position in the system, whether it is in the middle, beginning, or end because the ceiling in the basement is completed. Bleeding did not work and only produced cold water, even when trying to bleed large amounts. The length of the run of the cold radiator is approximately 7 feet (3 feet then a curve and another 4 feet). The control valve turns, but is very tight. I hope this gives you enough information. If not write back with some more questions. Thanks

Re: Cold Radiator


You'll have to do a very close inspection of the baseboard supply valve.

You say that it's hard to turn, but as I noted in the previous post, you'll have to determine if the valve is opening and closing properly.

Sometimes the little vertical brass metal stop directly under the handle gets snapped off and the valve travels too far when it is turned counterclockwise to open (thus re-closing the valve).

The (usually) round bakelite handle on the valve should turn no more than about 2" clockwise to CLOSE the valve; and turn no more than 2" COUNTERCLOCKWISE to open the valve.

If the valve keeps turning more than 2" in either direction without stopping, the metal stop is gone, and you'll have to try different positions to make sure you're actually opening the valve.

As long as the valve is turning, even though it turns hard, it's probably opening & closing.

You may have to use a mirror and a strong light to see the underside of the bakelite handle to see if the valve's metal stop is working.

If turning the valve in different positions doesn't restore heat, there's probably some other restriction in this particular baseboard or the associated piping that is causing the hot water in the main supply pipe to bypass it.

The next method to try is to shut off the water inlet valve at the boiler, bleed a gallon from the baseboard in question, remove the little bleed valve, and use a hand tire pump to pump some air into the line at that point; this may have to be done several times to be effective in restoring heat.

DO NOT use compressed air or a compressor to inject air into the lines.

This procedure often opens the line of any gunk particles that may be restricting hot water flow thru the BB.

If you're handy & want to try these methods, give it a shot; otherwise you may have to call a service person familiar with hot water systems.

It may be necessary to try a 3rd option, which is to open a panel in the finished basement ceiling to gain access to the piping that controls the baseboard and add another diverter tee on the risers that control the BB (there is usually only one diverter tee installed on these lines; 2 diverters would force more water thru the BB).

However, with a BB run of only 7 feet, one diverter valve is usually enough.

Other things a service person would be able to check once an access panel is available, is to make sure the diverter valve has not been installed backwards and that the supply riser to the BB is at least 2 feet away from the return riser as they come out of the main supply pipe.

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