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Hydronic Heating System Bypass

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@mjs: The boiler circulator is new.

UPDATE: I need a quick opinion.

I pulled the system circulator (Armstrong H51).  Here are some pictures.  There is an impeller, but the tips of the blades are worn (H51 impeller1, H51 impeller3 different).  By comparison, an H53 impeller has clean edges.  (The H53 has greater capacity.) All of the edges on the H51 show similar wear.  Only two are shown.

I suspect a little wear could affect efficiency, but this is my first time looking at the inside of a centrifugal water pump like these.

I am headed into Cleveland to get some parts (1-1/4" sweat x 1" MPT) that will be needed to install the Taco pump.  I am tempted to replace now but would like opinions from others.  Eventually I will replace as the Taco is quieter and nly 1/8 HP.  Right now, I need heat and hot water.

The one thing that drags on me is that until about 2 years ago, the system delivered plenty of heat.  Last year was not a good year to work on it, as getting outside help was difficult.


Hmm, not sure I can tell anything from those photos.  I'm not sure that is "wear" it might just be manufacturing imperfections.  I'd also take a good look at the mixing valve.  Is that thermostatic?  Computer-controlled? Can you observe the position of the valve from the outside?  If the pump is not massively worn, and the valve is opening, I can't see why you don't get hot water to the building loop.

Well, I am spending the night without heat.  The plumbing supply store that presumably had the fitting I need, didn't actually have it.  It will arrive tomorrow at noon.  My preferred solution is a 1-1/4" sweat x 1" MPT adapter.  They are made, but hard to find in Cleveland.  He claimed to have those, but misunderstood.  I can make it from 3 pieces, but space is quite tight and the difference between Taco and Armstrong pumps is only 5".

The mixing valve in the boiler is thermally controlled and seems to be working.  Otherwise, output from the boiler circulator would be greatly diminished.  If it is stuck open (maximum mixing), its replacement will require substantial dismantling of the boiler cabinet.  At that point, I think I would put up with the chill until Spring.  THere are no visual signs for its position.

Edit: Added the difference between Taco and Armstrong pump flanges (5").

Don't put a valve there, the close coupled tees are designed to create hydraulic separation - similar principle to a LLH.

If your boiler is short cycling then the issue is with the secondary circulator or the heating circuit. Can you measure the flow?

Thank you.  I sort of understand why one would not want such a pump running against a blanked off load or source.  What I don't understand is why the connection cannot be equal to the head of the maximum real load.  That is, why should it be the lowest load in the entire system?

I cannot measure the flow and investigated ultrasonic flowmeters, but was discouraged by a response that getting them set up is not as simple as YT videos suggest.

There is a ball valve between the bypass and intake to the boiler circulator as well as in the return line proper.  I believe that was in place to isolate the outside woodburner, which heats the return line, from the boiler so the boiler could be turned off completely.


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