New Hydronic Towel Rack Not Working

HeroBrian

Hi everyone; I'm hoping you can help. This is the short version of a very long story.

My house was built in 1928 and uses a two-pipe hot water system. I moved into the house ten years ago. Overall the system works well and we are happy with the hydronic heat in general but the two 9000BTU radiators in my finished attic never really got very warm relative to the radiators on the other floors. Even after reinsulating the entire 3rd floor did that space ever get really warm, say 62-65 deg on an average winter day—the radiators just don’t put out enough. The system pressure was 20psi and the top of the attic radiators are 30ft above the circulator, but even bumping this up to 25psi or so never helped very much (pressure relief valve is set to 30).

There is a huge primary trunk which goes off the boiler and feeds about four different circuits and all the radiators are roughly the same size. One circuit is capped off. The second one feeds three radiators on the first floor only. The third feeds the back of the house, two radiators on the first floor and two on the second floor. The last circuit feeds 5 radiators, three on the second floor and the two attic radiators in question. There was an ancient circulator on the main return trunk.

As part of a second-floor bathroom renovation, I had a HVAC contractor run new 1” pex lines from the basement to the third floor. The attic radiators were placed on these lines and the old lines were removed from second-floor vertical trunk lines and capped at the T. They put the new lines on a secondary circulator (Taco 007-SF5) with a zone controller and a new thermostat. I also had them upgrade the primary circulator (Taco 0013-MSF1-IFC) and put both circulators on the supply trunk *after* the compression tank ala Holden 101. Finally, I had them remove a small 3000 BTU radiator and its ¾” cast iron feed lines from the second-floor bathroom and hook up a Runtal hydronic towel warmer (Neptune NTR-4620) using ¾” pex. This took place in April 2019.

Immediately I had some issues. First, the primary circulator Taco 0013-MSF1-IFC is unbearably loud at any of its three speeds, but the lower the speed the louder it got. Second, the attic radiators were then so blazingly hot that one cannot even touch them almost all the time. This would happen even with the third floor thermostat shut off. This would happen regardless of the circulator speed. The new towel warmer however, worked.. good? It got pretty hot 2/3s of the way up then kinda tapered off…

I called back the contractor. It seemed obvious to me that they did not put a check-valve on the new attic circuit and when the primary circulator is on it was pulling water backwards through the new circuit. The contractor said this was impossible as the Taco 007-SF5 has integrated flow control. Taco says that it most certainly does not have this, but the contractor is insistent that it does. We proved the water was running backwards, the contractor shrugged his shoulders, said the check-valve was defective and replaced the pump with the same model. He also replaced the primary Taco 0013-MSF1-IFC with a Grundfos Type: UPS15-58FC, P/N 59896341P1. He said the Grundfoss isn’t as powerful but is “good enough” and much quieter.

He left somewhat abruptly, and didn’t review his work with me. It is true that the Grundfos pump is whisper quiet at any speed. The first and second floor radiators get nice and toasty. The third-floor radiators are also toasty and only when the new thermostat calls for heat, as expected. I can’t find any evidence of a new check valve on that circuit, so I’m unclear as to what changed there, but hey it’s working. But now the towel warmer does not heat at all. I’m still working on the bathroom and the floor is not screwed down so I can put my hand on the hot water supply line, which is hot, but no water is entering the towel warmer.

Zman

Do you have pictures of the boiler room piping? Trying to mix an old gravity system with new requires a contractor with some knowledge. That seems to be what you are lacking.

Ironman

From the date of your house, it looks like you have a converted gravity flow system. These systems usually work great if the balance of flow in the piping isn't disturbed, such as when converting to forced flow or attempting to combine new heat emitters.
When converting to forced flow, the upstairs radiators should have been checked for orrifice plates in the unions and if they were there, they should have been relocated to the downstairs rad's. This may be your first problem.
Second, if something new is added, it needs to be on a separate loop and circulator. It appears your contractor attempted to do this, but it has to be done in such a manner that the circulators and loops don't interfere with each other. Without seeing everything, it's not possible to tell if it's correctly done. Seems like not.
Posting some good pics, particularly of the near boiler piping and circs, would be helpful.

EBEBRATT-Ed

The towel warmer sounds like it might be air bound. You approach seems to be hit and miss, guessing. Hydronics doesn't respond well to that.

You need to sit down and draw out your system in detail, find the flow you need.....then go back into it to fix what is wrong

DZoro

A new towel rack should have a bleeder at the top. May look like, or even be a plug. I would inspect it carefully and think you will find one.
D