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Reasons for failure of cast iron rad to heat up after re-piping?

Posted by la_koala (My Page) on
Tue, Oct 4, 11 at 9:29

Hi,

As part of our kitchen remodel, the plumbers replaced the two vertical cast iron pipes going up to the cast iron radiator in the room above with Pex lines installed in the wall. Instead of the original pipes going straight up vertically, and then a short cross to each end of the radiator above, the Pex lines go up vertically between the studs in a wall about 6 feet away, then cross the 6 feet over to the original connections where the cast iron pipes went up into the radiator above.

They've refilled that zone of the system, and that's the only radiator that is stone cold. All of the others on the zone heat up.

The plumbers are suggesting putting in some sort of pump/regulator to pump to that radiator. Before they do that, I'd like a GardenWeb sanity check that what they're suggesting makes sense. :-)

My thoughts/questions:
- Is there any "directional" to these hot water cast iron radiators? I mean, do the need to make sure that what was the intake on one end in the original feeder pipe is the same intake in the replacement one? That it's feeding the same end of the radiator as it was before?
(I know there is for steam, however, this is hot water/radiant).

- Given that this radiator was working fine before, what about the new set-up would make it go cold now? The width of the Pex being smaller diameter? The greater horizontal distance going to the radiator from the vertical pipes now?

- Anything else that I should have them investigate before they jump to putting in this regulator item?

Thanks in advance!
Lee


Follow-Up Postings:

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RE: Reasons for failure of cast iron rad to heat up after re-pipi

My first thought would be the vent on the radiator is clogged, shut, or needs to be replaced.

Of course -- they SHOULD have used PEX with the same inside diameter as the previous pipe. If they used a smaller dimension, then it would need to be re-piped correctly.


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RE: Reasons for failure of cast iron rad to heat up after re-pipi

I know on some old radiators there is a small bleeder valve to let out air trapped in the system. Does your radiator have this and was the air let out?

Is the PEX still exposed? If so is it warm? If not then can you trace back to a point where the pipe is warm?

Is it possible one of the PEX lines as a kink in it?

Finally have the plumber explain why a pump needs to be added where one did not previously exist. I assume prior to the renovation this radiator heated properly. Something seems fishy about the the proposed solution.


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RE: Reasons for failure of cast iron rad to heat up after re-pipi

Hi, thanks for responding!

The radiator does have its air bleeder valve, and the air was let out.

My first thought would be the vent on the radiator is clogged, shut, or needs to be replaced.

Hi peteinsonj, by "vent on the radiator", do you mean the bleeder valve? Or something else?

Finally have the plumber explain why a pump needs to be added where one did not previously exist. I assume prior to the renovation this radiator heated properly.

This was my thought exactly! Prior to the reno, this radiator was a maybe a little slower than the other 3 on the second floor. However, it did heat up. My spouse says that during their heat test this morning, it remained completely cold.

Hi mike_home, yes, the PEX lines are still exposed. My understanding from what my spouse said happened is that the PEX lines were also cold, and they traced back to a point all the way back to the basement where the boiler feeds it. (Which makes me think that the issue is close to there, but, I could be wrong).

In terms of an explanation, the plumber is saying that this used to be a gravity-fed system, and then somewhere along the line, the owners put in multiple zones and circulators, so no wonder it needs a pump now. (Me: huh?). What I don't see is how it was working one way in May (given how cold and long our winter was), with all its same circulators and zones "stuff" and now is not working at all after their replacement work. :-)

Of course -- they SHOULD have used PEX with the same inside diameter as the previous pipe.

From looking at the PEX lines, I am pretty sure that they are *not* the same inside diameter as the previous pipes, but are smaller. The previous pipes were the old cast iron ones, that are 2 inches in diameter on the outside (there are still some in the house feeding the other radiators, so I can measure those). While I don't know what the diameter is inside the previous cast iron pipes, I would bet it was larger than the PEX lines.

So, peteinsonj, you probably hit the nail on the head with the diameter of the line.

Thanks again for your input! I'm not sure how to approach it now, but they're coming back for another heating test in the morning, so we'll see.


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RE: Reasons for failure of cast iron rad to heat up after re-pipi

If no lines are kinked and they tied the supply and return into the same tees that they were originally tied into it can only really be air. If the pipes are undersized you will still get flow but perhaps not enough. If the pipes are run above the radiation at any point and than back down the radiator bleed is worthless pretty much. They will have to find a way to purge the line of air now and in the future.
Glenn Hanson
Hanson Home Heating


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RE: Reasons for failure of cast iron rad to heat up after re-pipi

"The previous pipes were the old cast iron ones, that are 2 inches in diameter on the outside (there are still some in the house feeding the other radiators, so I can measure those). While I don't know what the diameter is inside the previous cast iron pipes, I would bet it was larger than the PEX lines. "

The smaller lines are likely not large enough for a gravity system, so now they want to try a pump.

Depending on the pump location it may still not do any good.

The water will flow easily in the old large lines, but not well in the smaller lines.
If the pump is for just that radiator it may work.


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RE: Reasons for failure of cast iron rad to heat up after re-pipi

I'm of the same thought as brickeye.

It sounds like this might have been a gravity system, and gravity is very sensitive to changes like this.

If they did this repiping without taking that into account, they owe you some money for the wasted effort, is my thought.


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RE: Reasons for failure of cast iron rad to heat up after re-pipi

Removing or re-piping old radiators takes some care and understanding of the old system. Flow will change with size of pipe. The cure may be a radiator specific circulator or balancing of flow through the remaining radiators.

Plumbers don't necessarily know boilers, just how to fit pipe in many cases. I would look to a boiler specific contractor.


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