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.

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.

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.

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

"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.

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.

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.

9 years later, but thought I'd add a thought based on what I am dealing with. It could be due to gravity etc or in my case, simpler and much more annoying.

I was dealing with the exact same story except we used per with the same diameter as the iron radiator pipes. The radiator was not heating at all. After many tests I let the valve open and drain constantly. What I found was the water began to heat up. Long story short, there is a blockage inside the radiator. We disconnected the radiator and placed it in the shower and tipped it on its side and shined a light through. Sure enough there is a nickle sized flake of iron probably a bur from the casting process that at some point detached. Augh! My next step will be to attempt to grab this thing with forceps and break it up. Anyway, super late I know but figured I'd mention for others.