Understanding tankless recirculating water heaters
Comments
-
I think I will have to get a plumber to run this test. It's weird how the kitchen sink and master bathroom are always pretty good. Every once in a while a long wait, a few times several minutes in the master shower. Both get very warm then hot and stay that way continuously. Only the 2nd & 3rd bathrooms get the cold water sandwich. And if I run the hot water at the sink for a couple minutes then the shower it's good enough, maybe 90% hot. The other thing is how both of these bathrooms during the cold water sandwich when you turn the valve off then back on you get a short blast of hot water turning cool in seconds. Like I said most times running the sink first minimizes or eliminates the cold water sandwich. The shower temperatures are never more than 90% hot usually they would be less.
Both bathrooms get their water from the hoses stubbed up from the slab in this chase. I put an access panel in during construction. No other home has this.
0 -
I think we buyers thought tankless is more efficient. Now I realize that when you have a recirculating system it may even be more expensive to operate.
It's also possible that me having the recirculating set to run 6am-10pm may contribute. It's also possible that the water heater operating like it is may be lowering my gas bill while only slightly raising the water bill.
0 -
@Ghost_Rider357 Are you able to post a picture further back to allow for the near boiler piping to be seen? I'm hoping to see if you have a piping issue there or at least a valve in the wrong position.
0 -
A couple of years ago, I installed the Moen 8372 HD as a shower/ tub valve:
Here is my review of the valve at that time. A one star review on Amazon:
Although this valve appears to be well designed, it has a material flaw due to the pressure balancing system that it employs. The valve has a certain amount of internal "leakage" between hot and cold under all conditions. Therefore, if you wish to have a full cold shower, this is impossible. Hot water leaks to the cold side immediately upon opening the valve. Additionally, the same thing occurs when the valve is set to full hot. There is some leakage of cold water which slightly dilutes the hot water. This requires elevated hot hot water temperatures to ensure a sufficient temperature to shower. It additionally compromises the temperature of the bathtub due to the dilution. I would never buy it if Moen actually disclosed this poor design and the compromises that one must make to utilize it. Unfortunately, it is now buried in the wall so extracting it and returning it is not worth the effort.
A discussion with Moen directly confirmed the above. That is how it is designed.
I would not make any conclusions regarding the flow from any single handle pressure balancing valve when one of the supplies is closed.
0 -
There's not much more than is in the picture above. I had these from when the plumber I hired thought the intake PVC was part of the problem.
1 -
Here's a better picture. I don't think it could be simpler than this.
0 -
Back to theorizing again. Would appreciate any opinions if these thoughts are possible.
Because of my experience messing with this. It seems that the kitchen, laundry sinks and master bathroom sinks and shower valves work pretty much as expected occasional longer wait times aside. It's only the two tubs that often have the cold water sandwich. Also my sandwich is more of an open face sandwich, meaning once it turns cold it doesn't get warm again.
Is it possible that one of the hot water lines stubbed up in the chase area (picture above) intentionally has a cold water connected with the hot water stubs. The reason I ask this is when I open all the hot water valves or even multiple hot water in the same bathroom the pressure pretty much stays the same but the water at the tubs turns 100% cold. And the change in temperature at the faucets is to quick for it to be done at the water heater. It like this is done to maintain water pressure above temperature. The other reason I think this is, initially in the morning when the cold water sandwich is the worst. It seems to me that if I let the tub valve just run after the initial 60% hot it gets cool, 20% hot and stays that way. It's only when I repressurize the lines by turning on the hot water at the bathroom sink then giving the recirculation pump a chance to get all the lines warmed up that the hot water at the two tubs get warm enough to shower???
0 -
@Ghost_Ride357 . Looking at your pictures I can see one that shows the two pipes connected to the cold side of the heater at the top and it looks like there is a swing check valve on the upper branch. THIS IS A PRIME SUSPECT for your problem. A swing check used on pex tubing is poor practice. Pex is hard if not impossible to keep straight or level when it is noodle soft hot or cold and bent. Replace it with a good quality spring check valve. That line that the swing check is on is "likey" a dedicated recirulation line. There's no recirc. purge valves or expansion tank and I can't see a relief valve though it might be there. I see pex connections on the lower ports in addition to the top connections but no service isolation valves. Is that lower connection blue pex with brass fittings being used as a condensate drain? If so, that's not good. The brass will fail at some point due to acidic condensate. I've seen it many times. Not a good quality installation. A good plumber can prove that the suspect check valve is not working in ten minutes or less.
2 -
Thank you Teemok this is very helpful information!
here 3 more pictures close ups to all the connections on top.
The top being the check valve. I also suspected this valve could be the culprit. I never would have thought brass would be a bad connector, what would be best?
I have a number to a new plumber so they can make the repairs.
What's your thoughts about this type of plumbing? The hose is good for freezes but when I saw all the crimp on connectors my thought was how often do those fail? In Chicago it was all copper. Pros and cons to everything.
0 -
If that check valve isn't doing it's job you'll get all kinds of havoc in the system. It could cause cold water out of the hot pipes.
The third picture looks to me like a Wye strainer cleanout.
2 -
just spit balling here, have you checked your washing machine? I had one do this to me and it was the internal solenoids not closing allowing water to cross connect. Also, do you have a hot and cold hose bib outside or a slop sink with a sprayer that could be left on periodically?
Tom
Montpelier Vt2 -
It's worth a try. I can shut off the laundry valves to see but the location of the laundry room suggests that it's probably not it.
I still think Teemok's idea of the check valve as making the most sense. At this point any idea is worth trying.
0 -
@Ghost_Rider357 The condensate drain should be all Plastic. 3/4 pvc is the typical. The idea is no clogs, kinks, or acid degradation. Pex is acid tolerant and there are plastic crimp fittings available. They just don' t flow chunks well and maintaining proper pitch is a bit harder with bendy pipe. At the least switch to plastic fittings and pressure flush them after maintenance work. I've seen large acid burn cuts in to concrete foundations where the brass fittings failed and no one notices, understands or cares.
There's nothing "wrong" with crimp pex connections. They are a bit flow restrictive in that they are smaller inside diameter than the pipe and there was a dezincification problem with brass fittings getting brittle. Easy to look up and learn about. Most new brass is better.
Good to see that relief valve there.
The programing for the recirculation pump can make a big difference. Some concepts of control are better than others. Make sure you fully understand and have vetted it's operation mode. The cold water sandwich will always be there to some extent. Predicable and small is the goal.
With hot water line running in the slab DHW recirculation can be expensive depending on how well its insulated. Narrowing the times of operation to just when really needed will help.
Push button on demand control is the best energy saving option. Edit add on: I have customers who eliminate the sandwich completely with push button control. They hit the button and know just how long to wait to find hot water at the tap and start showering before the recirc line gets fully hot. They catch the heater while it's on and there's no cold sandwich made.
3 -
I was able to speak with the plumber I hired, my neighbor hired them to replace the solenoid with error code.
His next suggestion is to open up all the hoses and blow air through them to check for a crossover.
Truth be told he doesn't know this kind of experience and from the sound of it no body else does either. It's not likely I'll be sending any more money their way. One thing he did say when I told him that the check valve may be defective. He said if that were true then all the faucets would be not working properly. That is mostly true the kitchen sink and master bathroom sinks and showers are mostly fine. When the wait time is a problem it's usually less than a minute or two. Once it's hot it stays hot.
Maybe the secondary bathrooms are last in the recirculating loop so they would be the first to be effected if the check valve was failing.
I think like all things with my brand new $600,000 house " I'll have to learn to live with it"
It sucks but from what I've been seeing it's just how the labor is, here.
0 -
Water ALWAYS follows the path of least resistance to get from internal pipe pressure to atmospheric. If it is easier for cold water ( the source of the internal pipe pressure ) to travel a path via the leaking or backwards tilted swing check through the hot water recirculation line to get to the faucet (and I assure you it many times is) …it will. You will experience warm to hot at first, do to the recirc. pump doing its job and while the heater might be starting up and the normal slug of Cold Water Sandwich is heading your way, so is the cold water from the continuous check valve fault. You see, a swing check relies on gravity to close its swinging door. That's fine if the valve is in an up flow, water lifts the door to open and gravity drops it to positively close it. When the valve is in the horizontal position or worse tilted so that gravity holds the door slightly open, it will not close the valve and the swinging door fails to "check" the water flow in the wrong direction. The easiest path for most of the water at other fixtures might be the normal route through the water heater so the problem with the swing check valve is less noticeable if at all.
1 -
Hi, If you could get your hands on a Flir One or other infra-red camera, it might give you some clues about what's really going on in the plumbing. The modern IR tools are quite sensitive, and almost certainly would show you any cold leaking into the hot side.
Yours, Larry
1 -
I put a level on the check valve and if anything it's back pitched a little. I get what you are saying about needing to be installed level and solid.
Not knowing how these devices work wouldn't the reverse water pressure close the flap?
0 -
Swing checks are notorious for not closing well, even when gravity is just right. That's why I previously said replace with a quality spring check valve.
"wouldn't the reverse water pressure close the flap?" Great question. The best answer is it depends. A piece of thread sealant or debris can hold it open. A bad hinge can hold it open. The velocity of the water flow and the position of the door determines the force on the door. Sometimes it closes it and other times it won't. If it's stuck full open, it has very little water flow force on it.
The door seal is a machined surface. There's no other seal. A corroded, contaminated or misaligned machined surface can prevent a good seal and after a leak path is established the metal surface can be eroded and a permanent increasing in size leak is created.
After years of experience with exactly this application of check valves, I would never put a swing check horizontally if it's at all possible. To be clear, spring checks also fail from time to time. Especially crap ones. Like the cobblers children's shoes I have an intermittently sticky 24 year old 1/2" spring check on my own recirc. line. Nothing like a honey do list to back burner.
2 -
It might take all of ten minutes to put a ball valve inline with that check valve — turn off the water, open a tap and let the water run out until the pressure dissipates, put a 5-gallon bucket under the line, cut the pex, slip crimp rings over the cut ends, insert a valve, crimp the rings. Turn the water back on and empty the bucket. In an exposed location like that I would have no problem using a SharkBite, which would be even quicker, like one minute. Something like this, 14 bucks on Amazon:
If you close the valve and turn off the circulator you can see if your problem goes away. If it does, bingo. If it doesn't, it's a good idea to have a valve there anyway so you can isolate the circulation return line so you can do maintenance without having to drain the whole system.
0 -
@DCContrarian Do that work to install a ball valve and leave the suspect swing check on bent pex in place? It's 3/4" pex anyway. Don't buy a 1/2" valve from that link. Do it once and do it right. Replace the swing with a spring and put a ball valve in if you like. He needs service ports to do any maintenance.
0 -
I see your point, but snipping that PEX and putting a sharkbite ball valve in is a DIY or handyman job, replacing the check valve gets into issues that require some plumbing knowledge, like what to do if the line is now too short after you cut out the old valve. I'd rather get a handle on identifying the problem before bringing in a pro.
If it were my house I'd be snipping the PEX and putting in isolation valves all over the place until the problem went away.
Don't see why you'd need a service port on the circulator line.
1 -
Hi @DCContrarian , I'm not sure if I'm answering the right question, but to your last point, I like to put in a drain valve to flush the recirc line, so that any air can be positively removed. Also, because of the usual slow flows through recirc systems, a lot of crud can build up there. Flushing tends to wipe the inside of the lines and remove that crud. 😎
Yours, Larry
1 -
Fair enough. I've never seen that. I would think that recirc lines would be less prone to crud than regular plumbing because they have continuous flow.
Usually with a tankless you have a service port on hot and cold for descaling. You'd want to shut off the recirc with a isolation valve while doing that maintenance. With an external circulator you'd also appreciate isolation valves around the pump in case it needs replacement.
0 -
Service ports to do any future maintenance. A suggested benefit of a ball valve in that spot. It would be good to have one there to change out a failed check. If doing all that, a tee with a hose bib ( per manufactures instructions for bleeding air from the line ) would be great too. I'm all for valves. By all means but for the same effort. https://www.homedepot.com/p/SharkBite-Max-3-4-in-Brass-Push-to-Connect-Check-Valve-UR2016A/323675912
with a ball valve, tee and hose bib if you like but the 3/4" check is the important thing.
edit: Larry beat me too it. Sorry for the repeat. Also, I'm in no way supporting the use of sharkbite type fittings but ya gotta do what ya gotta do.
1 -
You guys gave me a lot to think about. I need to get the tools to work on the PEX connections maybe watch some YouTube videos. I can install both very easily all the PEX is exposed in the closet.
0 -
I watched a video and talked with my brother who has a little experience he says Sharkbite is the way to go. He says you don't need to buy the crimping tool.
I don't mind buying a tool and doing it the best way possible. Amazon sells cheap ones not sure if the cheap ones are good enough. Looks like they come with everything I need except the go nogo tool.
You can see from the picture I can put both the new check valve and ball valve on the same line. I can even make up a bracket screwed to the drywall to support the valves.
0 -
Looking at the products I need. If I understand how it's installed the Sharkbite 3/4 push to connect check valve suggested by @Teemok would be a compression fitting no crimp tool needed. That would also make it replaceable later when it fails. The only tool needed is a PEX cutting tool.
If I buy the cheap kit on Amazon and the go nogo tool and a Apollo 3/4 ball valve. The difference in price between the Sharkbite ball valve nearly offsets the price of the kit. No doubt it's Harbor freight quality but with any luck I'll never need it again but would be nice to have if I do.
Also I don't really need the depth marking tool I just make a mark at 3/4 the normal pipe depth.
0 -
Hi, I have a bias. 😱 I don't like the insert type PEX fittings. There is substantial flow reduction caused by using them, as they are noticeably smaller inside than the expansion type fittings. The pressure differential they cause may be part of the problem you're experiencing. Insert 90s are the worst. Avoiding using 90s at all, by using bend supports where they will fit is best. another bias is Sharkbite fittings. They have good application as a temporary repair fitting, but I've seen them fail and cause much damage. Also, I have doubts about how long they will last in water treated with chlorine or chloramine. If you search Ebay for "uponor expansion tool", you'll see some deals on expansion tools. 😎
Yours, Larry
0 -
Larry if you are saying that you don't like press to fit connections. I'm with you. It's just a matter of time before something fails. I know from personal experience PEX can fail. We were in a rental a couple of years ago and the plumber fixed one and didn't verify that it wasn't leaking and it had a drip.
Looking at what home depot has. While they have both PEX b and Sharkbite ball valves I don't see a PEX b check valve.
In the past I learned the hard way. Just go to a plumbing supply and stay away from home Depot.
I would rather spend $100-200 more buying better parts and by installing it myself I'm way ahead.
I'm going to stop by my local supply and see if I can get all the stuff there.
You also a point about the connector pieces narrowing the internal diameter. I'm not sure it's going to make that much of a difference. I'm pretty sure the plumber used all PEX b fittings, so what's a couple more?
0 -
Better piping practice is always preferable. Solving your mixing problem should be the first aim. Doing that without re-piping the cold side with copper pipe and all the valves and even unions to make repairs and for getting the air out of the recirculation line isn't typically home owner feasible . So you are crimping or Shark biting or expanding type b pex.
Note: some type b manufacturers do allow expansion type fittings. (Nibco) Or pay a good plumber to stand by his work. Pick the poison.
also, If air gets in the recirculation line and it will, it will air lock and the circulator will not be able to do its job. This will add difficulty in diagnosing any other possible problems. If plumbing was easy everyone would do it and a good plumber wouldn't be worth more than an average lawyer.
1 -
That said I'll wait until I get a plumber. I wondered about how I would get the air out of the line once I cut off the old and added the valves. Perhaps air is in the line now. I'm no plumber but a retired carpenter with a fair amount of common sense.
0 -
I previously mentioned a Tee and a hose bib should be on the recirc line. The fitting stack starting from the recirc pipe heading towards the cold side heater connection is: Spring check valve with flow arrow towards the heater, then a Tee with a hose bib on the branch and then a ball valve then connect to the cold inlet line Tee. With the ball valve closed you open the hose bib with hose on it, water must flow from the recirc line and any air in it will come out with the flowing water. Once you have solid water with no more air, close the hose bib. Open the ball valve and open the hose bib again to burp any air that might be on the other side of the ball valve. Close the hose bib. That should do it.
That fitting stack could be all threaded together with crimp adapters on either end. Your recirc. line is over sized being 3/4" so the crimp fittings flow reduction factor doesn't matter at all. While getting rid of as many crimp fittings in your normal water flow path as you can and installing tankless service port valves would be best it's not required to get a working spring check valve, Tee with hose bib and ball valve in place.
1 -
@Teemok thanks again. So I went by the plumbing supply and got these parts. This makes sense to me and looks easy to install. He also said that the $30 Amazon kit would be fine for the tools.
1 -
Yikes! Here is a simple way to do it. A pex ball/ drain valve and a grip type check for easy disassembling. These T valves can purge from both directions.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
@Ghost_Rider357 There's nothing scary about your local store build. Plastic check valves and shark bite like connections are suspect but that's just my opinion. The dual direction purge ports are good but not necessary. You did fine. Threaded connections are fine. Use some thread sealant and tighten well. It's pex you can always cut add or replace fittings later if needed.
1 -
@Teemok thanks the parts store build seems like it will be easy enough. I planned on using Teflon tape and pipe dope. I have confidence in the threaded parts and I like there's only two PEX connections. The cost for all the parts was only $45
0 -
I think the tee and boiler drain need to be on the other side of the ball valve, based on the arrow on the check?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream2 -
@hot_rod Good catch! Drawings are better than words. I knew I should have posted one while I was writing. @Ghost_Rider357 The ball valve side is closest to the heater cold pipe and the arrow on the check points to the heater.
1 -
@hot_rod if I'm following you this is how you are suggesting that it be setup.
0 -
@Teemok I got my PEX tools today. I'm not sure these are what I want. I would rather use the PEX rings the plumber used a solid black steel ring.
These look a little cheaper. Maybe they are fine. I can return it to Amazon.
0
Categories
- All Categories
- 86K THE MAIN WALL
- 3.1K A-C, Heat Pumps & Refrigeration
- 52 Biomass
- 421 Carbon Monoxide Awareness
- 81 Chimneys & Flues
- 1.9K Domestic Hot Water
- 5.3K Gas Heating
- 96 Geothermal
- 154 Indoor-Air Quality
- 3.3K Oil Heating
- 60 Pipe Deterioration
- 894 Plumbing
- 5.9K Radiant Heating
- 379 Solar
- 14.7K Strictly Steam
- 3.2K Thermostats and Controls
- 52 Water Quality
- 41 Industry Classes
- 47 Job Opportunities
- 17 Recall Announcements