Author Topic: Hydronic Heating System Bypass  (Read 2636 times)

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Offline jpanhalt

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Hydronic Heating System Bypass
« on: December 07, 2021, 03:26:54 pm »
]Not sure whether this question belongs here or under "Power..."  It is not electronic; although all of the controls are and additional ones may be added.

Problem:  System heats slowly and cannot maintain an inside/outside temperature differential much above 40°F.

System (source: Weil-McLain installation manual):


My system was installed in 1993 and has had several modifications since.  The boiler is a Weil-McLain.  Specifically, I am questioning whether the highlighted connection between return and supply is needed and/or whether it should be a valve?  There is already an automatic bypass valve shown just below and labeled system temp control.  Boiler is bit shown but would be at the bottom of image.  Only its intake ("From System") and output ("To System") connections are shown.  That highlighted bypass is 1-1/4" copper pipe.  The To System is 1" pipe.  There is a circulator in the boiler and a second circulator  as shown (upper left) for the system.

What seems to be happening is the bypass creates its own loop.  Boiler fires, output is limited to 180°F, and shuts down, but the loop limits the temperature to the house circulator and radiators.  The boiler then cycles quite frequently (every 5 minutes or so).  Water to the house gets warm (about 60 to 70°F) but not hot.  Return water is is about 10°F cooler.

The system circulator is a 1/4HP Armstrong.  I have a replacement Taco 0011 pump handy, which should be more than adequate for the house, but it is not a simple bolt in job.

I am contemplating changing that direct connection with a ball valve that will allow adjusting the mix.  However, is that bypass even needed?  I would be easier just to plug it.   What are  your thoughts on that?
« Last Edit: December 07, 2021, 03:30:55 pm by jpanhalt »
 

Offline jmelson

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Re: Hydronic Heating System Bypass
« Reply #1 on: December 07, 2021, 05:10:09 pm »
Hmm, VERY strange.  I've never seen a setup like that.  It seems like this pipe would reduce flow through the boiler, and prevent it from delivering maximum heat transfer to the house loops.  My system certainly does not do that. the combination of all loops flow directly through the boiler.  The manufacturer may have had some reason to not want the full circulator flow to go through the boiler, but I can't imagine why.  It almost has to waste the heat generated and send it up the chimney.  OH, the note at the bottom right seems to imply there is ANOTHER circulator inside the boiler.  Then, it does make some sense.

As for your problem, there is something SERIOUSLY wrong, if the loop temp is only 60-70F!!!  Maybe the internal circulator pump has failed or the mixing valve has gotten stuck.  You might have to get a tech out who knows this manufacturer's system.

Jon
« Last Edit: December 07, 2021, 05:17:03 pm by jmelson »
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #2 on: December 07, 2021, 07:28:46 pm »
That loop temp was wrong.  It was a reading from a  HF IR cooking thermometer.  I thought about as soon as I left for Cleveland.  (I'm back now.)  Actually, it's between 115° to 125°F (guesstimate by feel).  That is, definitely warm, but not hot.  No where near 140°F (60°C).

The funny thing is, the US DOE (https://www.nrel.gov/docs/fy14osti/60200.pdf) shows a similar cross-connection:


But, there is only one cross-connection (my system has 2 in parallel), and the ostensible reason for that is to reduce condensation in the combustion chamber by increasing the temperature of the return water.  I understand what they are saying, but there is a 105,000 btu flame there too producing lots of water vapor.
 

Offline jmelson

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Re: Hydronic Heating System Bypass
« Reply #3 on: December 10, 2021, 03:38:36 pm »
That loop temp was wrong.  It was a reading from a  HF IR cooking thermometer.  I thought about as soon as I left for Cleveland.  (I'm back now.)  Actually, it's between 115° to 125°F (guesstimate by feel).  That is, definitely warm, but not hot.  No where near 140°F (60°C).Weaaa
Well, I can tell you I can't hold my hand on the loop pipes for even a fraction of a second when the system is running.  That has to be WAY over 125F.
So, your earlier diagram had a notation about a circulator pump INSIDE the furnace.  If that failed, it would certainly cause the problems you mention.  It could be just a controls issue, where that circulator is not being turned on.  If that pump is not working and you remived the bypass, it would turn it into a system just like I have here.  I have a 1975 system that is pretty original, 3 zone valves, one circulator.  I've rebuilt the circulator a couple times, replaced a few zone valves.
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #4 on: December 10, 2021, 04:42:34 pm »
@jmelson

Thank  you.  When I first bought the house in 2010, there was quite a differential between heated water from the house circulator and return water.  It is much less today.

Last weekend, I removed the Taco 007 circulator that was inside the boiler and replaced it with a new Taco 0010, which has a slightly larger capacity.  The 007 was OK.  My rationale was that a larger capacity pump from the boiler would shift the ratio of return to heated water to the house circulator in favor of heated water.

I got a little more heat, but then weather got cold. So, I left everything else alone.  Tomorrow is supposed to be above 50°F, and I plan to remove the larger Armstrong circulator and check it out.  I have a Taco 0011 (1/8 HP) to replace it with, if defective.  I may replace it anyway as the Armstrong is not maintenance free like the Taco.  I also have a ball valve to insert in the crossover, but it will be a tight fit with 1-1/4" copper pipe.  If that pump is defective, I will probably leave the ball valve installation until Spring. 

I did some playing with disconnecting one or the other pumps and looking for a temp differential across the pump.  In each case, the differential increased significantly across the non-running pump.  I interpreted that to mean the pump was working at least somewhat.   Both pump motors run and turn off and on simultaneously. 

I have also thought about getting one of the cheaper ultrasonic flow meters (see: https://www.eevblog.com/forum/chat/water-flow-in-pipe/msg3858407/#msg3858407 ) to assess relative flow, but have decided not to jump into that.
 

Offline jmelson

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Re: Hydronic Heating System Bypass
« Reply #5 on: December 10, 2021, 05:48:47 pm »
Well, maybe the thermostat in the boiler is failing.  It may be shutting off the burner before the boiler gets up to full temperature.  It kind of sounds like that may be the real issue.  The water on the outlet side of the boiler should be nearly at boiling temperature.  About 180 F.

Jon
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #6 on: December 10, 2021, 06:03:06 pm »
Yes, the high thermostat is set at 180°F.  It seems damn hot to me; although, I have not tested with a TC.  So, that shutdone seems OK.   I am looking to get the supply to the house (i.e., after mixing with any bypass) to 140°F (60°C) or above.  Something as high as 180°F would present a risk (small) for burns.
 

Offline jmelson

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Re: Hydronic Heating System Bypass
« Reply #7 on: December 11, 2021, 05:44:53 pm »
Well, maybe the impeller in the internal pump is wearing away, or the boiler is full of sediment.  SOMETHING is preventing the heat input to the boiler from getting out to the main loop.  That's what you need to solve.
Jon
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #8 on: December 11, 2021, 08:48:51 pm »
Hi Jon,

Thank you for the continued interest and suggestions.

Background (lengthy):
It's a complicated system -- much more than the usual installations.  In brief, the system of propane-fired boiler, indirect domestic HW, and house heat that I am using was not the primary system for the original builder/owner.   There were two additional sources of heat.  One was an indoor woodburner, which I never saw, and the other was a conventional outside woodburner.  The latter was in working condition when I bought the house.  The original builder relied on the inside woodburner for most of his heat, but probably used the propane boiler for domestic HW in the warmer months. 

The outside wood burner had its own circulator and is an open system.  That is, the wood burning boiler has a water jacket.  That heated water came into the house and transferred its heat to the house system with a heat exchanger.  The heat exchanger was in series with the return flow in the house and fed the house system through that crossover mentioned in my original post.  Thus, when the propane boiler was off, the high resistance of that forced most of the hot water to the house system pump.  The is also a manual ball valve that can isolate the return from the propane boiler so that resistance was not relied upon.

Since I no longer use the outside boiler, my initial question was whether that crossover was still needed, as its high flow of return water contributed to my cold house.

Back to the subject:
Both pumps work, and the new pump in the boiler, which has a slightly high capacity helped, but was not enough with 20°F outside temperatures.  The boiler seems OK.  There are 5 zones for the house proper and one zone for domestic HW.  There is another zonie for the whole house that must be open for the individual zones to get full heat.  When the domestic HW zone valve is open, the main house zone valve is (was) closed.  Having that priority seems logical.  The return line form the domestic HW gets quite warm and feeds the main return line directly. The problem that I discovered yesterday is that the domestic HW zone valve almost never closed -- even when I was not using hot water.  Apparently, its temperature was set high enough that during cold spells, the stay warm setting was never reached.

As a test, I disconnected power to the main house zone valve and manually opened it.  I got much better heat  last night.  Every room was at its set temperature.  It's too warm today to do much more, but this morning, I lowered the temp setting on the domestic HW, and the system is acting more as I would expect.  The circulating pumps at least turn off, and heated water to the house zones is much warmer.  As a temporary measure, I may leave it like that or play with the domestic HW setting and reattach  power to the whole-house zone valve.

I have not liked the indirectly heated HW since I moved here.  In warm months (most of the year in my area), it seems foolish to run a 105,000 btu boiler just to take a bath or wash dishes.  I have toyed with the idea of replacing it with a conventional hot water heater.  This episode may be enough to get me over my reluctance.

The answer to your "SOMETHING" appears to have been the zone valve to the whole house.
 

Offline jmelson

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Re: Hydronic Heating System Bypass
« Reply #9 on: December 13, 2021, 04:31:20 pm »

As a test, I disconnected power to the main house zone valve and manually opened it.  I got much better heat  last night.  Every room was at its set temperature.  It's too warm today to do much more, but this morning, I lowered the temp setting on the domestic HW, and the system is acting more as I would expect.  The circulating pumps at least turn off, and heated water to the house zones is much warmer.  As a temporary measure, I may leave it like that or play with the domestic HW setting and reattach  power to the whole-house zone valve.

I have not liked the indirectly heated HW since I moved here.  In warm months (most of the year in my area), it seems foolish to run a 105,000 btu boiler just to take a bath or wash dishes.  I have toyed with the idea of replacing it with a conventional hot water heater.  This episode may be enough to get me over my reluctance.

The answer to your "SOMETHING" appears to have been the zone valve to the whole house.
Very interesting!  Well, that explains the complexity of the system.  So, we have had problems here with old zone valves sticking.  Every 5 years or so, something goes wrong with one, and we have to at least replace part of the valve. Sometimes the inside of the valve, sometimes just the actuator, so we don't have to break into the water system.

Sometimes just operating the manual override on the valve will loosen the bindup.  Yes, I agree the domestic hot water/furnace tie in doesn't make any sense when building heat is not in use!  ESPECIALLY with propane!  Possible an electric hot water heater would be more cost effective, rather than propane.  As for the bypass, you could put a ball valve in there so you could adjust the amount of bypass.
Maybe just pull the extra pump and mixing valve out of the system, and make it a classic hydronic system.
Jon
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #10 on: December 13, 2021, 08:05:32 pm »
Every change has made a little improvement.  Tomorrow's plan is to remove the big Armstrong pump, which feeds the whole house and DHW, and check it our.  I didn't want to dig into that at 3:00 PM local.  Replacing it with a new Taco will require actual plumbing changes.  A good part of today was spent driving to Lowes and Menards and getting some anticipated parts -- about 3 hours.  Replaced the pressure release valve on the boiler, which was leaking, and looked into the boiler.  Seems fine.

With the system cool and refilled, that pump heated very slowly.  Maybe it is working just by convection.  Will update.
 
John
 

Online floobydust

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Re: Hydronic Heating System Bypass
« Reply #11 on: December 14, 2021, 02:03:17 am »
The boiler controller has an outdoor reset? Just got mine fixed, the thermistor was reading about 10-15C degrees warmer than it actually was outdoors. So the boiler water temp was cool and sometimes intermittently going in warm weather shutdown.
Argued with a few HVAC contractors for two years. Turns out it was cracked cable with some water in it. It needed to be shielded twisted-pair but ground not connected to earth-ground but just to the (floating) Tekmar controller input. The guy put it in conduit and seems OK for now.
I would make sure the boiler water temp is bang on because it can be a goose chase.
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #12 on: December 14, 2021, 06:11:08 am »
There is no outside temperature gauge or reset for the propane-fired boiler.*  The circulator in the boiler runs and gets up to water temperature.  That system gauge is mechanical and seems reasonably accurate.   That is, at 180°F, I cannot keep a finger on it.  Flow from the boiler goes directly to the system circulator  (see diagram in first post).  Both circulators always run simultaneously whenever a room thermostat or DHW call for heat.  The only temperature control outside the boiler and room thermostats is called an "Aquastat."   It is on the main return pipe and shuts down the boiler when a set temperature for the return is reached.  Currently, that setting is 160°F.  Return temperature remains well below that now.

The problem is that heat from the boiler loop is not getting to the various zones in the house.  The zone values, which are in the return lines, do seem to operate as expected.  That is, when the thermostat for a valve is calling for heat, the temperature of the corresponding source pipe increases.  Albeit with the current problem, it only gets a little warmer.

John

*The outside wood burner does have its own temp gauges, controls, and circulator, but that system is isolated and disconnected at present.
 

Online floobydust

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Re: Hydronic Heating System Bypass
« Reply #13 on: December 14, 2021, 06:33:42 am »
About the bypass on the boiler, it is a mysterious thing because you would think water would just not bother flowing through the boiler and just take the bypass route.
On one boiler here there is instead a ball valve as the bypass and I played around with it. If you close the valve, more flow through the boiler, greater delta T in temperature but it cavitates when closed a fair bit. As if the boiler cannot take full flow. If you open the ball valve, the boiler short-cycles because temperature comes up fast, it has too much heat for the amount of flow. I was told a boiler has efficiency curves and a factory-recommended delta T across it and that determines the ball valve setting.
For the same boiler with a double T-fitting (bypass) I asked how that works and was told the water density difference between boiler inlet and outlet due to the temperature difference is enough to make the denser cold water go into the boiler instead of bypassing it.  There's some physics involved. Taco has proportional valves for the bypass I don't know much about them.

Another troubleshooting technique is using a thermal imaging camera to see what is going on. It sounds like you have restricted flow from a lazy zone valve or too much plumbing and maybe a booster pump would help if the boiler is seeing too much outlet pressure impeding flow. You have to know the pump curves. A "bigger" pump may not do much better than a small pump if pressure difference (inlet and outlet) I think is big.  A Bell & Gossett has a flat pump curve, meaning same medium flow rate regardless of delta P.
I was thinking of your system acting like there is a kink in the garden hose. Bigger pump still can't do much.

Sometimes these hydronic systems are poorly designed and never work that great from day #1.
« Last Edit: December 14, 2021, 06:38:15 am by floobydust »
 
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Offline mjs

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Re: Hydronic Heating System Bypass
« Reply #14 on: December 14, 2021, 10:06:54 am »
Check out the boiler circulator pump.

The system functions likely like this (I know district heating systems better than propane..)
- When the boiler is off, the circulation goes through the straight connection. Let's say this flow is 20 lpm.
- When the boiler is on, its circulation pump causes part of the flow to go through boiler circuit instead of straight connection piece
- The shunt valve in the boiler circuit (usually a three way mixing valve here) is used to limit/control the temperature going out from the boiler loop to distribution loop

Since the heating loop circulation pump is 'sucking' from the straight connection, the flow coming from the boiler loop goes rather to the heating loop than back to boiler loop.

The reason for having a separate flow in the heat delivery circuit is that the water mass also acts as a heating energy buffer. You can even use a buffer tank to increase the capacity and reduce the duty cycle of the heat source.
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #15 on: December 14, 2021, 04:53:26 pm »
@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.

John
« Last Edit: December 14, 2021, 04:55:26 pm by jpanhalt »
 

Offline jmelson

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Re: Hydronic Heating System Bypass
« Reply #16 on: December 14, 2021, 06:52:04 pm »
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.
Jon
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #17 on: December 14, 2021, 07:30:55 pm »
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").
 
« Last Edit: December 14, 2021, 10:02:38 pm by jpanhalt »
 

Offline SteveyG

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Re: Hydronic Heating System Bypass
« Reply #18 on: December 14, 2021, 09:38:57 pm »
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?
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #19 on: December 14, 2021, 10:00:35 pm »
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.
 

Offline SteveyG

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Re: Hydronic Heating System Bypass
« Reply #20 on: December 15, 2021, 09:06:32 am »
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.
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #21 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).

« Last Edit: December 15, 2021, 10:25:34 am by jpanhalt »
 

Offline jmelson

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Re: Hydronic Heating System Bypass
« Reply #22 on: December 15, 2021, 04:08:33 pm »
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).
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.
Jon
 
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Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #23 on: December 16, 2021, 10:05:38 pm »
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.

John

PS: The electrical wiring is temporary.  I was desperate.
« Last Edit: December 16, 2021, 10:09:58 pm by jpanhalt »
 

Offline jpanhalt

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Re: Hydronic Heating System Bypass
« Reply #24 on: December 17, 2021, 08:59:37 pm »
UPDATE
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.

John

« Last Edit: December 17, 2021, 09:03:58 pm by jpanhalt »
 


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