Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Troubleshooting water not flowing to a rad [pipe map included]

blu_in_green Member Posts: 11
Thanks to the help from you all in my other thread, I'm getting ready to rebuild my boiler side to be "pumping away."

Before I do this, I want to try to solve another persistent problem where one rad doesn't receive any flow. I've attached a map that tries to show the layout and the smorgasbord of piping currently in place.

Some notes:
- This is a very old 2 pipe system with one circulator that has had rads added at different points over the years.
- Generally the house seemed to heat fine through the winter aside from the single rad identified as the problem rad which received no flow (when I tried disconnecting one of the pipes it looked like water was in the pipe but it wouldn't gush out or flow out even into the open air).
- This rad is fed by 1/2 pex Tee'd off a busy line
- The pex also runs up through the wall, into the ceiling joist and back down to feed the rad (I'm wondering if this loop is creating an air pocket).
- A couple of the basement rads are also fed by pex running through roof joists and back down into the rad, but they don't seem to have any issue receiving flow and heat.
- Only 2 of the newer copper lines have balancing (ball) valves; none of the steel have balancing valves. There are no zone valves. All balancing is done with the valves on the rads.

I have basement tenants so major pipe re-running is not possible, but boiler side work (balancing/zone valves, etc) is possible.


  • Jamie Hall
    Jamie Hall Member Posts: 23,443
    Probably is an air pocket... but. If you disconnected the line, and there was water sitting there but it didn't flow you may simply not have quite enough pressure to handle those loops which go up and come back down. So... the question is, what pressure is your system running at? If I understand your description correctly, the top of that loop is probably a good 16 feet about the basement level. You will need at least 15 psi in the basement at the inlet to the pump to get water to flow up and over the loop consistently. The other radiators which loop up and back down like that illustrate that once flow is established, with no leaks, it will keep going despite the pressure being too low -- but you can't get it to start a flow that way.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • blu_in_green
    blu_in_green Member Posts: 11
    I think about 16 feet vertical is correct.

    The system is typically around 12psi cold and 15 warm, but my gauge may be slightly inaccurate. When I had my expansion tank off (accidentally) I was pushing system pressures of 20-25 hot but still wasn't getting flow that I'm aware of at that problem rad.

    Not sure if any of this changes your thoughts on the problem.

    Earlier on I one of the other "looping line" Rads seem to lagg behind, but for other reasons I had to drain and refill the system and the problem went away. All the other "looping rads" are in the basement so that might explain why they aren't as much of an issue...
  • Jamie Hall
    Jamie Hall Member Posts: 23,443
    If there's air in that loop -- and I'll be mightily surprised if there isn't -- it's not going to come out easily, and even with adequate pressure it won't, at least easily. Assuming there is no way to bleed it at the top of the loop, you are going to have to somehow get a lot of flow going into that one loop from the bottom -- all the other radiators will have to be off. Otherwise, any flow is just going to go somewhere else, quite happily.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • blu_in_green
    blu_in_green Member Posts: 11
    Are there any other recommendations for improvements at the boiler side when this work is undertaken? What I'm thinking...

    - Isolating (ball?) valves for the circulator to allow for work.
    - Remove the line constrictions near the boiler that narrow to ~1" at the boiler.
    - Replace circulator with a variable speed model such as Grundfos Alpha 1 or 2.
    - replace expansion tank with a modern diaphragm model with some sort of air separator and "pump away."
    - What about balancing or zone valves?

    Q1: Recognizing I'm not going for perfection, and can only work in the boiler room and at the rads themselves: What am I missing?

    Q2: Does anyone recommend a particular circulator model, air separator, balancing/zone valve model/brands?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,105
    edited June 2020
    So you have 2" main piping from an original system. This tells me that the original system that was installed by some "Dead Men" designed it without the need for a circulator pump. (gravity system with low flow rate thru each radiator and hand-fired with constant flame. No thermostat required ) Later on someone replaces the boiler, added radiators and included a circulator in no particular order. Now you have a radiator that does not heat. The fact that there is little or no flow when the piping is disconnected is of concern.

    My go to text for solving problems like this is a book called Zoning Made Easy. http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf
    Page 7 illustrates that the circulator pump does not actually "Pump" water up to the radiator as you might think. Imagine a fire truck pumper pushing water up to a nozzle on a ladder, then the water comes out under pressure and falls to the ground. That pump must be very powerful to get the pressure up that high with that much force. That would be very noisy in your heating system.

    The circulator pump in your heater is more like the motor on the Ferris Wheel, just bearly strong enough to push the water in a circle. The weight of the water going up is offset by the weight of the water going down. So the pump does not work that hard. If you have air at the top of the column of water (the pipe feeding the radiator) your circulator pump can only lift it a few inches or so. then the flow stops (or to be more accurate never actually started).

    The fact that there is little or no water flow at the top radiator when disconnected, tells me there is probably some air in that radiator when connected, or the pipe feeding the radiator has a blockage.

    Do both feed and return pipes on the problem radiator have the same "No Flow" condition? If so, then the water pressure in the basement is not enough to fill the radiator. If only one has the condition, then you have a blockage. This will be a project to determine. You will need a large basin, and connect a hose from the radiator feed and return pipes so the water will flow into the basin. A portable sump pump can be placed in the basin to keep it from overflowing. Now raise the pressure in the boiler and monitor the flow out of both feed and return from the radiator.

    If you find a blockage, air pressure from a compressor can be used to backpressure the blocked pipe or tubing. If lucky, the blockage will break up and find its way back to the boiler and settle there.

    Let's assume it is just a water pressure problem. Now you need to operate your system at a higher pressure, Pumping away from the expansion tank will help with that. Set the pressures to say 18psi and the circulator pump will increase the pressure to that radiator, no problem with getting too close to the relief valve pressure this way.

    Now we need to resolve the flow rate. Is the feed and return to the problem radiator a small pipe or a pipe from the old original system? If it is a new smaller pipe then we need to reduce the flow rate to all the radiators on the original big pipe radiators. By closing the radiator valves on the radiators with less resistance to say 20% open, the pressure to the problem radiator will increase getting more flow

    I solved a similar problem in a Cape May NJ Bread and Breakfast by installing Non-electric thermostatic radiator valves on the radiators that were overheating when the room heated by the "Problem " radiator was comfortable. see the description on page 20 of zoning made easy.

    Your problem may be as easy as near boiler piping upgraded to "Pumping Away".

    I hope this helps with your understanding of how the heat flows in your system

    Ed Y

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?