How to automatically vent domestic hot water recirculation loop

[Jamesplumbing06]

Also learned a long time to stop hearing the customer and start listening. Homeowner descriptions are very tricky. Do people normally see steam that builds in system.? No but they all do. This should be a normal system and he never have to bleed. But he is bleeding because water turns cold. With the system I see. I see so many ways cold water could into hot side and cause someone to over investigate. Every hot water system builds pressure by way of forcing molecules apart almost to the point of a gas. This makes the water look lighter giving impression of seeing bubbly air. So if everyone with a circ system bleed it once a month then yeah everyone would think they see air. But all of us know that with a pressured system the only way to physically get water in is to introduce a higher pressure air. Either during repair or city malfunction. But neither of those happen every month like clock work. So I am identifying this problem as I see it. It’s a mess and waste of money and time. I would spend the time to do it as a plumbing book says. Not a manufactures book. Of course they tell you it’s correct. Remember valveman? Manufactures tell you their truth not the truth. So forgive me not reading word for word. I would be wasting a lot of people’s money if I did everything they had an idea for. This system is over complicated and I can get the same results with half the cost and same quality material. I know a scam when I see one. The residential mixer valves are stupid. Turn the heater up. If you see steam. Turn cold on more. Then touch it. Why install yet another valve to waste money and maintain and throw every theory of a problem out the window until the plumber sees that. You can’t properly diagnose a system with that many parts in the way. Even running heaters parallel you have to get the developed length perfect and still take a chance at using only 1 heater while the other just sits there. I can promise without looking. This is not a parallel return line. Even with the globe valves (which are against code) you can’t possibly expect proper flow thru both lines all the time

 

[Diehard]

Oh, by the way. An automatic air relief is just a small chamber with a float that closes the vent when the water is in it. When air finds it way up there, it lowers the float by lowering the water level and opens that little vent hole on the top. Fills with water again and closes.
Thee are very many different designs depending on size, application, etc.

 

[Diehard]

Also learned a long time to stop hearing the customer and start listening. Homeowner descriptions are very tricky. Do people normally see steam that builds in system.? No but they all do. This should be a normal system and he never have to bleed. But he is bleeding because water turns cold. With the system I see. I see so many ways cold water could into hot side and cause someone to over investigate. Every hot water system builds pressure by way of forcing molecules apart almost to the point of a gas. This makes the water look lighter giving impression of seeing bubbly air. So if everyone with a circ system bleed it once a month then yeah everyone would think they see air. But all of us know that with a pressured system the only way to physically get water in is to introduce a higher pressure air. Either during repair or city malfunction. But neither of those happen every month like clock work. So I am identifying this problem as I see it. It’s a mess and waste of money and time. I would spend the time to do it as a plumbing book says. Not a manufactures book. Of course they tell you it’s correct. Remember valveman? Manufactures tell you their truth not the truth. So forgive me not reading word for word. I would be wasting a lot of people’s money if I did everything they had an idea for. This system is over complicated and I can get the same results with half the cost and same quality material. I know a scam when I see one. The residential mixer valves are stupid. Turn the heater up. If you see steam. Turn cold on more. Then touch it. Why install yet another valve to waste money and maintain and throw every theory of a problem out the window until the plumber sees that. You can’t properly diagnose a system with that many parts in the way. Even running heaters parallel you have to get the developed length perfect and still take a chance at using only 1 heater while the other just sits there. I can promise without looking. This is not a parallel return line. Even with the globe valves (which are against code) you can’t possibly expect proper flow thru both lines all the time

Apparently multiple returns is quite common. Maybe not in residential but in big buildings. They use balancing valves and other methods to help in distributing the hot water reasonably equal.
The OP is only using one of those two return loops. The other is shut off.

 

[ExtraMilePlumbing]

I would install a check valve after the pump ,that's all I got with my 6 years on the job lol.ill show our senior plumbers this see what they think

 

[frodo]

you should not need a bleeder valve, it is not a closed loop system
issues
aqua stat is closer than 5' from heater--false readings
globe valves instead of ball valves,
you need to tie into the bottom of heater, not the top

your picture shows the return [circ] tied into the cold inlet side of the wh
with out a ck valve one the cold inlet.

 

[Greenthorn]

I really appreciate the input and will try to address some of the comments/suggestions. I was busy with my day job carpentering the last few days. I work on high end to uber high end homes and always make a point of checking out the mechanical room (AKA submarine). Some of the layouts I see leave me in awe because of how carefully they are built. I have immense respect for any honest plumber.

There is no substitute for experience. Lacking that, I consulted the most reliable resource in the world: Youtube There are plenty of videos there posted by people who claim to be experts. I went way down the rabbit hole and watched them all. Some of the most informative and interesting are put out by Caleffi- they do periodic webinars attended by professional plumbers and engineers. Here are a few examples:

Hot Water Recirculation Systems webinar:


Installing Thermostatic Mixing Valves & Recirculating Pumps in Plumbing Systems webinar:



Caleffi also has very clear written descriptions of the options available for various fittings and devices. And Caleffi makes exactly the device that would be better than globe valves for balancing my 2 loop system: they call it a Thermosetter and the reasons for using them are described in this video:


Here is a pdf describing the Tank mixer I installed and love:
https://www.caleffi.com/sites/default/files/file/01267_17_na-r4.pdf

and HERE is the diagram that is the main source for my layout:
https://www.plumbingforums.com/media/mix-recirc.661/


I may come across as a disciple of Caleffi, but they really are the only company I'm aware of that takes the time to explain fully the use and need for their devices. If their excellent videos and written materials are the way they are able to market their products, then more power to them.

On the other hand, Grundfos, which makes the pumps I see in 95% of houses, including mine (#98420223, Model UP10-16 A PM BN5/LC) has terrible to nonexistent information about their devices. The cartoon they provide for installation instructions is really a joke:
https://us.grundfos.com/content/dam/GPU/Products/98563206_0614_Grundfos_Comfort_US_QG.pdf
I could write pages filled with expletives about that, but the physical characteristics of my pump are pretty cool.

OK, back to the original posting and problem...

Diehard asks, "What size pump do you have? GPM vs. discharge head"
Here is one of the more informative parts of the installation instructions:
https://www.plumbingforums.com/media/head-flow.662/

Jamesplumbing says, "Once air is properly evacuated then you will never “build “air again."
and
Diehard asks, "Are you sure you're purging all the air out of the complete system when you do it?"
Answer: When I first tried the pump and it was clearly cavitating, I turned on all the faucets in the house and set them on hot in an attempt to purge the system. That didn't work enough to get the pump primed and functioning properly, and is why I installed the hose bib near the pump. I have only purged a gallon or so of water at a time through the hose bib, but it is always enough to get the pump working for another week or two.

Jamesplumbing is understandably perplexed by the complexity of the system and dubious about the need for all the stuff. I agree that some of the ball valves are probably excessive. We could start a fun thread called plumbers vs. engineers/parts manufacturers... But, with all due respect, I think you may fail to understand the need for and benefits I'm getting from the tank mixer. I challenge you to describe a simpler method for safely getting more hot water from my heater. Understand that the showers in my house are old two valve types. I learned as a child to avoid being scalded in the shower just from the sounds coming from the plumbing, but I don't want to put my kids through the same trial. You also just don't want 140 degree water available at single handle faucets, and I'm not going to install a mixer at each of those locations.

ExtraMilePlumbing says,"I would try keeping it simple by only having the pump,hose bib and check valve.and you need a cross over tee in tha farthest fixture for that comfort series pump"
I do have a cross over near the farthest fixture in the loop that is active. The other loop is a stub for future work so, in effect, I have a single loop system for now. The problems in balancing the 2 loops could be the source of a future posting I agree with the idea of keeping the system as simple as possible. But I do think there is a reason for each of the elements in the system.

So, after all that, here is where I stand:
1. Maybe I never purged all the air.
2. Maybe heated water is releasing air that is collecting in the high point in the system and the little pump can't push it out through the faucets.

I think both are possible, but I think #2 is the problem that needs to be solved.

 

[Greenthorn]

you should not need a bleeder valve, it is not a closed loop system
issues
aqua stat is closer than 5' from heater--false readings
globe valves instead of ball valves,
you need to tie into the bottom of heater, not the top

your picture shows the return [circ] tied into the cold inlet side of the wh
with out a ck valve one the cold inlet.

"aqua stat is closer than 5' from heater--false readings"
According to my reading of the pump instruction cartoon, the aqua stat must be placed 8-20 inches from the water heater. Where precisely do you suggest I put it if you think it's in the wrong place?

"globe valves instead of ball valves"
The globe valves are, to my knowledge, vastly better at adjusting flow than ball valves, and better than gate valves. Isn't a globe valve just what an old two handle faucet uses?
Jamesplumbing says globe valves are against code. I am a novice in that regard, but ask that he quote both the code and the actual reason for it.

"you need to tie into the bottom of heater, not the top"
There are different reasons when and why you might tie in to the bottom, but the tank mixer I'm using is designed to be plumbed in to the top of the water heater. I think it is a more elegant method and will allow eventual replacement of the water heater with less fuss. Given that I am running the water heater at 140 degrees, replacement will come sooner. That is a trade off I'm willing to accept in order to get more hot water and quit having to schedule laundry, dishes, showers, baths, etc. I also like the idea of having the sediment down near the water heater drain and away from my expensive pump.

"with out a ck valve one the cold inlet"
I think the check valves are where they need to be but if you think there needs to be one between the pump and water heater, please elaborate.

 

[Greenthorn]

I would install a check valve after the pump ,that's all I got with my 6 years on the job lol.ill show our senior plumbers this see what they think

Between Frodo and ExtraMilePlumbing, I'm considering the utility of a check valve after the pump. Can you explain why you think that will solve the problem?

 

[Greenthorn]

Frodo says, "aqua stat is closer than 5' from heater--false readings"

This is a different subject, but one I've thought about quite a bit...

Regarding the aqua stat, I think ideally it should be installed near the farthest fixture for a single loop system. This may require a different method of utilizing temperature information than is typical, but the whole point of a recirculation system is to have hot water at the fixtures. If you compare the temperature of the water as it leaves the water heater with the temperature of the water in the recirculation loop at the farthest fixture, you could control the pump the way it should actually be controlled. As soon as there is hot water available at the farthest faucet, the pump should turn off. I believe the pump uses both an internal temperature sensor and the aqua stat for control, but I don't understand quite how.

This brings up one of the problems with the Grundfos pump: Auto Adapt. They claim to have an ingenious set of instructions that the pump uses to learn the water use habits over a period of 2 weeks. If you dig into the technical information, you can glean a little about how they do it. I am not convinced that the pump can learn enough about water use habits to be right more than 80% of the time- there are all sorts of possible exceptions to the past 2 weeks of usage. Also, if the pump loses power, it loses all the data it uses to decide when to turn on and off, and you start over. I understand if some people are happy with the system working most of the time, but I want it to just work as efficiently as possible all the time. I don't want to wonder if the pump has decided whether I want to wait for hot water each time I turn on the tap.

My pump has 3 operation modes:
1. Temperature- I don't understand exactly how it decides when to turn on and off, but it is using temperature information.
2. Auto adapt- as described above. Insanity comes in all forms.
3. 100%- if the pump has power, then it is pumping

I use the Temperature mode. Once I have solved the original problem, then I might get into the control aspect more.

 

[ExtraMilePlumbing]

A check valve in between heater and pump prevents cold water from pushing back against hot water been pulled from pump(defeating the purpose of the pump).(most pumps dont have build in check valves)also i hope you are using spring loaded ck valves and not those swing valves that get stuck open)

 

[Greenthorn]

A check valve in between heater and pump prevents cold water from pushing back against hot water been pulled from pump(defeating the purpose of the pump).(most pumps dont have build in check valves)also i hope you are using spring loaded ck valves and not those swing valves that get stuck open)

The pump does not have an internal check valve. Both of the check valves on the other side of the pump are spring type.
However, as I understand it, the pump does not have to "work against cold water pushing back against hot water". If it did, I doubt the system would ever work. Remember that the system works perfectly for weeks at a time and only one recirculation loop is in use. When it quits, I purge some water with the hose bib near the pump, then it works again flawlessly for weeks more.

I do consider the possibility that a check valve after the pump would keep air from reaching the pump, but its purpose is to allow water to flow in only one direction, not to prevent movement of air, and I am not very confident it would help. My money is still on the need for a vent at the high point. I think the water heater is releasing air from the city water, and it is rising to a high point in the recirculation loop, eventually creating a big enough zone of air that the pump can't move water through it.

At this point I need to just try it out and report back.

 

[Diehard]

.

 

[Diehard]

Cold water is supplied to the tank bottom through a dip tube.

What are you guys calling an Aquastat?
Are you talking about what appears to be a temperature sensor connected to the HW line leaving the tank, and which is wired back the the pump? If that's what it is, I would have thought it would be on the return recirculation line entering the pump.
Of course not much of any of these comments have anything to do with the problem of apparent airlock.

 

[frodo]

A ball valve/ circuit setter is industry standard for setting hydronic systems
the reasons are you get full flow with out obstruction, and the biggest reason is the lack of maintenance required on ball valves, a globe vale is a directional valve that must be installed in one direction and it uses a rubber ''bib'' washer that wears out and the screws loosens over time causing a 'chatter' in the piping that is a sob to figure out what it is.


As far as the orientation of your pump, you have installed the pump in a air loop trap that is always going to trap air

 

[frodo]

Cold water is supplied to the tank bottom through a dip tube.

What are you guys calling an Aquastat?
Are you talking about what appears to be a temperature sensor connected to the HW line leaving the tank, and which is wired back the the pump? If that's what it is, I would have thought it would be on the return recirculation line entering the pump.
Of course not much of any of these comments have anything to do with the problem of apparent airlock.

you are exactly correct, the sensor needs to be on the return line from the house

that way it tells the pump...hey man,,,this water is not hot, wake your butt up and circ this line

the way it is installed right now is the pump is sensing the water is nice and warm, and does not need to come on

I have installed 100's of circ lines and pumps using engineered drawings and no drawings
the pump is always down low. hummmm i wonder why? could it be that it is not installed in a loop above the heater where air will always migrate to?

look at this air loop

 

[Diehard]

Also, it seems to me, that ball valve between the pump and the connection to the CW to the tank, must be closed to properly purge the system. Like I had mentioned earlier, with that valve open, drawing off water from that draw-off above the pump is simply getting the cold water through that open ball valve, directly to the pump without going through the entire loop.

 

[Greenthorn]

Cold water is supplied to the tank bottom through a dip tube.

What are you guys calling an Aquastat?
Are you talking about what appears to be a temperature sensor connected to the HW line leaving the tank, and which is wired back the the pump? If that's what it is, I would have thought it would be on the return recirculation line entering the pump.
Of course not much of any of these comments have anything to do with the problem of apparent airlock.

You're probably right that I am calling an aquastat (which is a temperature controlled switch) what is actually a temperature sensor. If only there were instructions with actual words that came with the pump I might have been more accurate. By the way, I am probably misusing the term "cavitation" as well- a better term is probably "air lock" that many have used. Anyway, instead of clear instructions with a side of useful information, here is everything that is available from Grundfos about the sensor and where to put it:

Sensor

• Greenthorn
• Nov 17, 2018

Grundfos sensor location instructions

As I said before, and I'm not sure this is correct, I think the pump has an internal sensor that senses the return temperature. Frodo, if you have knowledge related to this pump, please spill it forth and elucidate us, the heathen populace.

I will repeat that the system works flawlessly for a week or two, then fails completely. That means that, as you see it plumbed in the photo, any and every time I go to use hot water, it is there within a few seconds, and that it doesn't change at all until when that week or two is up, it is no more worky. I have the pump plugged in to a Kill-a-Watt device and listen to it each time I go by. There is no change in the pump sound or the power usage when the system changes from working to not working. I then purge a gallon or so of water through the hose bib, and everything works great for a week or two.

 

[Greenthorn]

Also, it seems to me, that ball valve between the pump and the connection to the CW to the tank, must be closed to properly purge the system. Like I had mentioned earlier, with that valve open, drawing off water from that draw-off above the pump is simply getting the cold water through that open ball valve, directly to the pump without going through the entire loop.

The last time I purged the system, I closed the valve below the pump, and opened the hose bib and let a gallon or so of water out. That worked just fine and I've seen several days now of the system working fine.
I'm trying to use some of the information I've gotten in this thread (thank you again) to figure out the problem. A month ago, I would purge the system by first closing one valve near the pump and flushing water through the hose bib, then opening that valve and closing the other valve near the pump. I wasn't being as scientific, but the system worked, so I could just go back to playing solitaire for a while.

 

[frodo]

can you give us the name and model of your pump
then i can goggle it, i might see something that has been missed


as far as aqua stats..i rarely use them
i run a wire back to the bathroom. to the light switch.
when the light comes on the pump circs water. saves energy that way

please tell me which way the arrows on the check valves and on the globe valves are pointed
is the pump pumping to the water heater?

what is the hot water pressure with out the pump running?

i play spider. can you beat 2 minutes 53 seconds?
only did it one time..

 

[Greenthorn]

Frodo, you may see this covered earlier in the thread:

- The pump is a Grundfos #98420223, Model UP10-16 A PM BN5/LC
I would be extremely grateful if anyone could find some details about the pump brain and sensors. How about start by explaining page 8 of the installation instructions:


- Arrows on check valves and globe valves point to pump. One globe valve is currently completely open (for the existing plumbing) and one globe valve is completely closed (future work and possibly another discussion on balancing a 2 loop system).


I want to just throw it out there again that I think this stuff is both very complicated and interesting. I spent a great deal of time researching and planning my system. The return line has sat unused for 4 years while I completed my plan and found the time to plumb it. There were stacks of specifications, drawings, ideas, and notes. Despite some criticism, mostly from Jamesplumbing, I will argue that my system is pretty darn good- I am the customer and the customer will be very much pleased once the issue at hand is resolved.

I like your idea about a wire to the bathroom switch, and would be interested to hear more details about your pump, pipe sizes and lengths, etc. But my pump at a max flow of 1.5 gpm would take forever to pull hot water all the way from the water heater through the roughly 50' of 3/4" supply pipe and to the farthest fixture in the house (well, actually the volume of that water is 1.15 gallons, so at least 45 seconds). For some, that might be just what is desired. As I mentioned, the control issue is a whole other topic.

The static water pressure in my house is 70 psi.