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Hydronic Heating System Bypass

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The close coupled tees performs multiple actions, though it depends on the system as to how useful they are.
Firstly, it allows the boiler to maintain it's set temperature differential and correct flow rate regardless of system load, but the primary function is hydraulic separation. It means you can run multiple circulators on a system where you have differing requirements for each circuit or where the primary circulator doesn't have head to overcome resistance in the heating circuit.

Given you only have one circulation pump on the primary flow, I suspect it was installed this way to maintain the minimum flow rate through the boiler. Think of it as impedance matching.

Thanks, Steve for that explanation.  Quite helpful and prompted me to lookup a Taco mixing valve.  This description follows what you say, plus a little more about the return and system (Notes 2&3).


--- Quote from: jpanhalt on December 15, 2021, 10:23:02 am ---Thanks, Steve for that explanation.  Quite helpful and prompted me to lookup a Taco mixing valve.  This description follows what you say, plus a little more about the return and system (Notes 2&3).

--- End quote ---
WOW!  That sure looks like their "balancing valve" is what you were proposing to put in the shunt pipe.  This is all VERY different than the systems I am familiar with.

Three nights without heat or hot water, and I got the Taco 0011-F4 installed.  The original fittings for the Armstrong were off by 1/2" left-to-right and 3/8" front to back.  The top piping is a little crooked, but I was desperate for some heat.  The key for a simple installation was two, 1-1/4" sweat x 1" MPT adapters, which I had to special order and got late yesterday.  Photo attached.

It is working somewhat but is not much better than before.  I am thinking the bypass on the boiler may be the culprit (as mentioned before), but that valve has been obsolete for a long time.  Weil-McLain has a service bulletin for it, but I could not find it on W-M's website.  Sent an email Tuesday night to W-M, but have not heard back.  Current W-M systems do not have that valve. 

Of course, a lot of air was/is in the system.  I will continue to vent it after running overnight.  The good news is that the Taco is silent. Even Though it runs almost continuously, I do not hear it, and it does not spit oil at the DHW heater behind it.

Regards and thanks for the advice.


PS: The electrical wiring is temporary.  I was desperate.

I have dug extensively through installation and service manuals.  A "mixing valve" was used in GV boilers, series 1 and 2, but not 3 and 4.  Mine is a series 1.  There's a note in the service manual to refer to Service Bulletin SB0401R1.  That is not on the Weil-McLain website, so I sent an inquiry Tuesday  hoping to get a reply.  Nothing.  Called Tech Service today, and the engineer I spoke with said it was not on the web site, but was in an archive folder he had. (I hate it when companies do such things.  Storage is so cheap.)  He sent me a pdf, and since it is so hard to get, I am attaching it in full to this post.  Manye other Googlers will benefit. 

The meat of the SB is to disable the mixing valve and instructions are given there-in.  Now for the interesting part.  For large systems with an expected return temperature of less than 130°F, a modification of the system is recommended.

Note the addition of two, bypass adjusting valves.  One is in a close-coupled T; the other in the supply line.  I took a day off today[attach=2] (Friday) and will attempt the disabling tomorrow.

NB: There is still a close-coupled T in that drawing that is not regulated.



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