Only half of my Radiator heats up

mcp1

I recently had one of my old cast iron steam radiators refinished. It was dipped in an acid bath, sand blasted, primed & painted; it looks great. When i hooked it back up, only 2 or 3 of the rails are heating up out of the 9 rails on the radiator. What would cause this? I'm not sure if there's a blockage or what. Hopefully someone has some suggestions on how to get the heat to the rest of the radiator.
Thanks

JUGHNE

Is there a working air vent on the radiator?

mcp1

Yes, I have a Danfoss thermostatic radiator vent on it. The vent is set at 4. The radiator is located on my 2nd floor and the riser only supplies this radiator.

Jamie Hall

And did your refinishing and painting people leave the opening for the air vent open? Or paint it shut?

mcp1

The opening for the air vent was open. I replaced the vent when i reinstalled the radiator.

Jamie Hall

Just a vent? Or a Danfoss thermostatic radiator valve? And if the latter, to what do you have it set?

mcp1

It's a Danfoss thermostatic radiator valve set at 4

Jamie Hall

OK -- then the question is, is the room getting to the temperature you want? If it is, the Danfoss is doing exactly what it's supposed to do: close the venting when the room is up to temperature. No need to have the radiator pumping out heat that you don't want...

JUGHNE

Can we see a picture of the radiator showing both ends?

Fred

I'm hearing at least two changes here. 1) the radiator was removed and refinished, which isn't likely to be the source of the problem or 2) the vent was replaced with a Danfoss thermostatic vent. Either that vent is working like it should (if the room is up to temp) or the setting needs to be increased or the vent isn't working at all and the steam is compressing the air in the radiator enough to allow 2 or 3 tubes to heat up. In any case, I think the issue is at the vent.
I suppose there is a third possibility, that the supply valve isn't fully open or when you did open it, the disc inside the supply valve came loose and isn't letting steam into the radiator.

mcp1

Thanks for the feedback guys. I'll put up a picture. Fred, how would i know if the Danfoss vent is working? I'm going to set the vent at 5 and see if that does anything. If the vent isn't working should i replace it with a varivalve vent?

Fred

mcp1 said:

Thanks for the feedback guys. I'll put up a picture. Fred, how would i know if the Danfoss vent is working? I'm going to set the vent at 5 and see if that does anything. If the vent isn't working should i replace it with a varivalve vent?

Don't replace it with the Varivent. They are so aggressive that they will spit water. You can use the Vent-Rite #1 or the Hoffman #1A. Both are adjustable.
About the only way I know of to test the Danfoss is to take it off and use one of the two vents I suggested and see if that fixes the problem.

mcp1

JUGHNE

You have to keep in mind that the TRV-air vent you have will only shut off the heat by preventing air venting, not call the boiler to come on for more heat. The boiler has to shut down for it to open and start over.
If you turn it up all the way does it heat more?

Jamie Hall

Seems we haven't answered the fundamental question when using a temperature controlled vent -- is the temperature in the space what you want?

mcp1

Jughne, I turned up the vent and now I'm waiting to see if that works

mcp1

Jamie, when using the Danfoss vent the temp is not what i would like the room to be. I would like the room temp to be warmer.

Jamie Hall

mcp1 said:

Jamie, when using the Danfoss vent the temp is not what i would like the room to be. I would like the room temp to be warmer.

Turn it up. If your boiler cycles often enough, that will work (the boiler has to cycle off for the TRV to reset).

I presume that you couldn't control the heat properly with a conventional vent?

JUGHNE

Adjust it higher and try it for a couple of days, these are not an immediate response device.

Jamie Hall

I might add -- there is a common misconception with TRVs that if you turn it up you will get heat. Doesn't work that way. If you turn it up, it will let the radiator heat longer -- the next time the boiler turns on. Further, it is quite possible that the actual vent you have attached to the TRV is too small to let the radiator heat enough anyway.

mcp1

You guys are a big help, thanks!!!