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Radiant zone not working after service, and really odd piping configuration

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I live in a two-family and recently had a plumber relocate some radiator pipes from my neighbors system to clear headroom in my basement, and since that work my neighbors have stated that their radiant zone is not working. I'm really stumped as to what might be going on, and even more stumped by how their system is designed, and I'm hoping someone can help me out. I've attached a diagram for reference.

Their system is a Burnham Alpine boiler, with Zone 1 serving about 8 cast iron radiators, and Zone 2 serving a radiant tile floor in the kitchen, which just has a single tube supplying the floor. A taco zone controller is used to turn on the boiler, and it is not set up to give zone 1 priority.

The boiler also has an indirect DHW tank, which has its own circulator, and gets priority over central heat. The boiler circ will run when Zone 1 or Zone 2 call for heat, but not when there is a call for DHW.

The plumber had to relocate some radiator piping and drained the boiler on a few times to do so. When my neighbor said their radiant zone wasn't working, I monitored the system and noticed that when just the radiant zone called for heat, the boiler heated up in a minute or two, then shut down because it reached operating temperature, pipes servicing the radiant zone stayed cold. I assume there might be some air in the lines, so I opened the radiant purge valve (labeled "B" in the diagram, and the water just came out in a slow trickle, not anything like the full 20 psi I’d expect. After I did this, though, the zone started to get some hot water through it and heat up, almost like I cleared an air pocket or created a syphon. This is the only way I can get flow through the zone – by purging the radiant loop for a few seconds. It seems to behave a bit better when Zone 1 is running, but it still doesn’t seem like it’s getting adequate flow.

I assume this is related to the recent relocation of pipes, but since our cold weather lined up exactly when the plumbers did the service, I can’t say with 100% certainty that the floor was working properly before the service. I do know, however, that it was functional last winter.

What really confuses me is the plumbing of the mixing valve on the radiant loop. The boiler supply water is connected after the mixed port. Once I get water flowing through the zone, the temperature of the water supplying the radiant zone does seems to track with the adjustments I make to the TMV, but does this piping configuration make sense to anyone, and any thoughts as to what the problem might be?

It seems to be like the flow/pressure in the line is just way too low, so I’m thinking either a major air pocket or a bad circulator. The 1/25 hp pump draws about ½ an amp, which sounds about right, so I’m not sure what to check next. I could try hooking a hose up to the radiant loop in an attempt to push out any air, but that’s not exactly easy given how the system is plumbed. I'd have to modify the pipes to add a connection.

Neighbors are looking at me (or a plumber) to solve the problem, but I’m having trouble understanding the issue because of the TMV piping. Any thoughts are appreciated!

Also worth noting that the plumbers who did the work have not been helpful. They said they purged the lines and it heated up, which I’m sure it did, based on the tests I did, but it’s not working as intended. I’m trying to get them back to the house, but my guess is that they’re going to pass the buck, and say they have no way of confirming it worked before they serviced the system. Thanks for the help!



Comments

  • Zman
    Zman Member Posts: 7,573
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    How much did the plumbers change?
    Did you close the valve to the right of the circ when you opened A. Can you manually override your fill valve when you purge to get higher flows?
    The piping of the radiant loop is not ideal and is making your circulator airlock. If it worked before it should again once the air is out.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • grant_andrew
    grant_andrew Member Posts: 22
    edited November 2019
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    Thanks Zman. All they did was relocate some pipes that feed radiators on zone 1, but they had to do it over the course of a couple trips, so the whole system was drained and refilled a few times.

    I didn't close the valve after the circulator when I opened the purge valve - I'll try that tonight. I guess I didn't think that would matter, since it's a closed system and theoretically should be the same pressure everywhere.

    I'm thinking I can tee in a hose connection after valve A, and isolate the radiant loop from the rest of the system and purge it with higher pressure water, since my auto-fill doesn't have an override.

  • Zman
    Zman Member Posts: 7,573
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    You want to make sure you are moving the water through the radiant loop. Without the valve closed, the water may be sneaking back through the circ.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • grant_andrew
    grant_andrew Member Posts: 22
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    Just to follow up on this, the problem ended up being the circulator. At one point, the plumbers had left a valve "A" closed and let the system run, until I noticed it a few days later. I'm guessing that burned the circulator out. It's working now.

    There are still pretty major swings in temperature, which tells me the TMV isn't working right, and I'm guessing it's because it's either faulty, or just a result of it being plumbed so oddly. I'm going to suggest that we re-pipe it as shown below. The changes are shown in the clouded area. Any issues?