Understanding tankless recirculating water heaters
I was directed here from another forum. I have been having difficulty finding information to help me understand what has been happening with my tankless water heater.
When we moved into our new house. That has a Bradford and White tankless recirculating water heater. It seemed to work correctly for about 6 months. We were hearing about dozens of failing water heaters out of 70 new houses. FF to today they may have replaced as many as 36 of them maybe more. All similar issues primarily long wait times, inconsistent hot water temperature, I recently learned is called "cold water sandwich" others including ours a year ago suddenly get scalding hot water. At the time we were told we had a cracked solenoid. The builder's plumber replaced it under warranty.
We continued to have long wait times and other weird issues. Later the plumber told me that the problem is B&W came out with a improved model and installed 1000 of them, ours being one of them. Then they discovered a problem and updated the design and he has been a victim here because he has been having to replace them for free, eating the labor cost. He also told me when the heaters display on error code the unit can be replaced in a half an hour otherwise it takes hours to go through the diagnostic process to figure out what is happening.
So anybody with a error code gets a new water heater. Dozens, like us have the same basic issues but no code we have been told your warranty is up and you have to get it fixed on your own.
Our multiple issues one as far as I can tell is only at our house. The hot water is at the kitchen sink and the master bathroom is pretty consistent with occasional long waits a few times it was more than 8 -10 minutes having ice cold water. I ended up turning the unit off and on letting it recycle and was able to get hot water again. Often mostly if I get a shower at odd times during the day, say early afternoon after mowing the lawn. It will take a long time to get hot and I just get a cold shower and it warms up about half way through.
Here's the weird part that no one has been able to explain, neither plumber or the B&W Rep. In the 2nd and 3rd bathrooms the tub faucets when I turn them on "all" hot pretty much anytime but it may be worse in the morning. In seconds it's warm and suddenly it turns cold and stay cold. If I turn it off and back on within seconds it turns 90% hot only to turn cold again. This happens continuously, turning it off and back on again. Also in those bathrooms if you turn on both the sinks and tub one or both will turn completely cold. I have noticed that if several hot water valves are open it becomes warm possibly cold.
The builder's plumber was going to give me a new water heater but when he realized I had no codes and after showing him that scenario he stopped the replacement and said it must be the one of the 5 faucet cartridges in the house and that is part of home maintenance. Basically I'm on my own call a plumber.
So I did. He seemed like a knowledgeable guy and he over two different days diagnosed and came up with a few possibilities. He changed the 2nd and 3rd bathroom tub cartridges, changed a 1/2 inch flexible gas line to a 3/4 and fixed a better option for the intake PVC pipe.
Now I'm up to $595.00 and nothing is fixed. The plumber I hired also had the rep come and look at it during the 2nd day of work. I told him about the dozens that I'm aware of that have either been replaced or are still having problems. Last I talked to my plumber he was also suggesting that maybe the hot and cold water hoses got crossed but that is only a guess. He said he knows the builders plumber and would have to consult with him to try and figure out what might be going on.
Because it seemed to work normally for the first 6 months I don't think it was plumbed wrong. I think something is wrong with the water heater and because of how it was plumbed the 2nd and 3rd bathrooms react differently than the kitchen sink and master bathroom.
But really I have no idea what or how much it will cost to just blindly try and fix this.
I have learned for the most part how to live with it. If you run the 2nd and 3rd bathroom sinks hot for a few minutes then take a shower the temperature stays a constant 90% hot never 100%. I also turned the temperature up to 125deg and all hot at the kitchen is near scalding once in a while but never in the the bathrooms and certainly not in the secondary bathrooms.
Sorry for the long text and hopefully someone will have some answers for my complex issues.
Comments
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If it was mine I would toss it out and install a tank type water heater. Some will recommend a heat pump water heater, but they have their own issues, and I am sure you are sick of water heater issues.
I agree with you that if it worked right for the first 6 months the plumbing is likely ok but a faulty cartridge could cause some strange issues. Maybe @Larry Weingarten and others will have some ideas.
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Did they check the temperature of the hot water leaving the water heater to confirm that the water heater is causing the issue. just because you have hot water issues doesn't always mean its the water heater. you need to narrow down your search
Does your hot water system have a recirculation line?
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I think now that the has been plumbed for a circulating system it would be costly to convert it to a tanked noncirculating system plus the length of time to get warm then hot water would become annoying. On the plus side we already set it to circulate 6am to 10pm and the most of the time the water in the pipes is around 50-70% hot sometimes often taking 30+ seconds to get that warm. If I had to I can live with this. The biggest problem is when we have guests we have to tell them to run the sink hot water first. I have recently showered in these and it seems to work but never more than 90% hot, but warm enough.
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Hi, Some thoughts. We need to see if the problem is with the heater, the plumbing, or both. A good test of the plumbing is to shut off water to the heater and then open any hot tap. Does water stop running in a few seconds? If it keeps running, there is a crossover between hot and cold which needs to be fixed. Is there a tempering valve?
About recirculation: is there a separate pump for moving water through the hot plumbing? Can you give us some photos of the heater and connecting plumbing? If there is a recirculating system and if it isn't done right, it could be a big part of the problem. Just for your information, it's hard to get recirculation to work well with tankless heaters for multiple reasons. Recirc can work just fine with a tank.
I'm guessing your heater has a screen at the inlet. Screens get dirty, slowing flow, and this can make the heater very unhappy, which it will be sure to let you know. Has the screen been cleaned recently?
Yours, Larry
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I think I need to see a diagram of the plumbing involved here. Without that, I — at least — would find it hard to pinpoint the problem.
Other than a rather fundamental problem: tankless water heaters and recirculation systems are contradictory. The whole concept of the tankless is to take the flow to the hot water fixture or fixtures and, with a very large power source, heat it from a cold source to hot as it passes through the heater. The whole concept of the recirculation system is take a source of hot water — a tank full of it — and recirculate it slowly through the hot water (and return) pipes, so the water in the pipes is always hot, and hot water is available at the tap immediately. There is a low power source in the tank to reheat the tank from time to time to keep it in the desired temperature range.
They don't mix.
In the meantime, is there a check valve on the return line for the recirculation?
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England3 -
"Other than a rather fundamental problem: tankless water heaters and recirculation systems are contradictory."
That was my first thought when I read the thread. I bet if you read the manual for the heater it specifically says not to try to run it with a circulator.
How about putting a 5-gallon electric tank downstream of the tankless? Run the recirculation into the small tank, let it handle the standby losses, the tankless only runs when there is real demand for hot water. It would probably help even out the temperature output of the tankless as well.
Call it "semi-tankless."
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Thanks Larry,
This is very good information. Are you suggesting that I turn off both the heater and the inlet valve, shown in the picture? I'm pretty sure that just powering it down will not stop the the water flow. Turning both off sounds like a very good test. Even a rookie mistake that none of the plumbers or the company rep knew.
I will say this, the homes that had replacements are no longer having issues.
The other two pictures are in a chase, that I have access to. You can see multiple hot and cold lines coming up from the slab. Hot on one side cold the other. All of these directly to all 3 sinks and one of the tubs for the 2nd and 3rd bathrooms.
I have lots of pictures during construction showing the water hoses.
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The specific water heater is a Bradford and White Infiniti tankless L-series model RTGL199N1 the recirculating pump is built into the unit.
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Assuming that the two tub cartridges I replaced are good. Should I consider taking the 2 original cartridges and replace two of three in the master shower?
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I presume you have the manual for the appliance? If not, it's here.
Go through it with a fine tooth comb. Make sur3e that the installation is complete and correct. Make sure that the check valve (if this is a dedicated mode recirculation system) is correct, in place, and working. If this is a bypass mode system, check that the bypass valves are working correctly.
There is a pretty extensive trouble shooting section. Go through that with an open mind…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England2 -
Now we are getting somewhere!!!
Thanks for suggesting going through the manual. When I shut off the cold water intake to the water heater I went around and checked all the hot water valves. The kitchen sink, laundry room sink, 2nd and 3rd bathrooms all had a few seconds of drips and stopped as did the sinks in the master bathroom. In the master shower all 3 have continuous drips and no cold water either. Just verified that all 5 tub/shower valves don't have cold water either, not in the normal way. The sinks all have normal cold water and nothing but a few drips of hot.
Again makes me wonder are these rookie mistakes how did neither plumber or the B &W rep not know this test.
I think that my next test is to replace each cartridge in the master bathroom one at a time. Then preform the same test looking for difference.
The picture of the shower shows the valves all 3 bathrooms have and that all 3 in the picture are dripping continuously.
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"In the master shower all 3 have continuous drips and no cold water either. Just verified that all 5 tub/shower valves don't have cold water either, not in the normal way. "
I would expect that the shower valves are pressure-balanced to prevent scalding. So when the hot water is off there would be at most a small trickle of cold water.
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In 2nd and 3rd bathrooms it's just a few drops. What I meant when I said normal way is, in these bathrooms when I turn the valve to cold I can get a spert of cold then it stops. In the master all 3 just keep dripping pretty much the same whether they are all hot or a mixture of cold.
That sounds like the pressure balance you are talking about. Still the master shower is different than the other two bathrooms. So that's pointing to it being the problem. The house is only 18 months old so is it worth changing the 3 cartridges in the master, perhaps with new. Or does swapping them one at a time using the ones from the other two bathrooms a more sensible start?
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I still don't understand your description. What problem do you think is happening, and how do you think changing the cartridge will fix it?
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If the unit worked correctly for six months, I would suspect it is the heater and not the cartridges. Of course, water quality can make a difference in cartridge performance.
When I have situation such as your, I will routinely look at the electrical. I will disconnect all plugs and receptacles and spray them with Electronic Cleaner that you can get at Walmart or any auto parts store.
I then reconnect them while still wet with cleaner. Do this with no power to the unit and one connector at a time. This includes the circuit board. It's surprising how this will many times return a unit back to correct functioning. Try it what have you got to lose, six bucks and a little time.
As an added note, I have had this kind of problem with the HTP Munchkin boiler's Molex connectors to the circuit board and I replaced the offending Molex female connector to the circuit board pin with a new one which corrected the problem. I can't tell you why the offending Molex connector wouldn't pass the current to the pin but it solved the problem.
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I have been told by the plumbers that sometimes the cartridges fail and allow the cold water to mix with the hot. I would want to change them to rule out that they are not causing the water to bleed through.
Because according to the manual the master shower should not have cold bleeding through. Suggesting that I have a crossed pipe.
I said it was working normally for 6 months. The fact is that we rarely used those bathrooms so who knows for sure.
The other thing is the long wait times that happens at odd times during the day.
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It takes a minimum amount of flow for the units to trigger on and heat consistently. Could the shower heads be too restrictive? A partially plugged inlet stainer can cause these issues also.
What is the water pressure in the home?
Is there a thermostatic mixing valve in or on the hot outlet of them heater?
Tub shower valves can be pressure balance or temperature and pressure balance type. If you have hard water the cartridges may need routine cleaning to keep them working accurately.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream2 -
I'm hopeful that at least one of my water heater issues is fixed.
I already paid the my plumber to replace 2 cartridges, part of the $595.
Nothing improved so you would think the 2 original cartridges are good. I contacted the builder's plumber he was adamant that the it is a bad cartridge not a crossover. He told me a way to tell which cartridge might be bad being correct 90% of the time.
It didn't work for me but I changed out 2 of 3 in the master shower and just by chance the 2nd total of 4 have now been changed or switched.
Huge improvement in the temperature in the 2nd and 3rd bathrooms. Starts out warm within seconds it starts getting hot and for the first time it starts getting uncomfortably hot. I have it set to 125 degrees.
However I redid the test I found in the manual I posted yesterday and the master shower appears to keep dripping indefinitely.
It will take a couple of days to make a judgement but I'm hoping it's fixed.
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It's looking like things are definitely improving. Talking with a friend and other posts I've read makes me think this is a case of the effects of hard water. A friend that's been living in the area for a while told me about a house annually he to soak the cartridges in vinegar. He said it's a good idea to turn the water back on with the cartridge removed to clear the line out.
That makes sense in a way because it's one of two valves we use daily. I'm going to change the 5 valve cartridge. That's the one my wife uses mostly. Then soak both cartridges in vinegar and put them up and wait till things get wacky again.
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I know of cases where thermostatic mixing valves need deliming every 6 months. Same with tankless heaters.
It depends on how hard the water is, how hot you run the heater, and how much water passes through the valve.
Maybe consider a water softener on the hot, or one of the other water conditioning methods, TAC for example.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
I spoke to soon a day later it seems to be the same as before. It boggles my mind how this is happening.
Why does it seem to work at different times of the day? It seems that in the morning I turn on one of the secondary bathroom tubs the temperature is warm then turns cold and stays cold for a long time several minutes if I leave it alone. When I turn the valve off then back on I get a blast of hot water and then it turns cold again. If I run the sink first then the the tub it works better.
It seems like there is a crossover, mistake by the builder's plumber. He refuses to think that is possible. He still says it's a cartridge. I've changed 2 rotated the other 3 and I still have the same issues.
So my three choices are, spent 4K and get a new water heater and maybe nothing will change because it's plumbed wrong, spent thousands to do forensic research to try and figure out what was plumbed wrong, or I can just live with a f***d up system.
Eventually I will have to replace the water heater sooner or later. I could wait until then but if I wait till then I won't be able to take the builder or his plumber to court. Something I'm not sure I'm up I did speak with a lawyer and make no mistake would be an up hill climb costing thousands and even if I win might not recover legal costs.
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Do your shower valves have stop valves in them? Valves that shut off the water so you can work on it without turning off the house water? Usually they're part of the valve body and turn with a flat-head screwdriver.
Crossover between hot and cold water can cause a lot of mysterious behavior and can be tricky to find. If you shut off the hot and open a tap you should be able to see if crossover is happening, water comes out of the hot. Sometimes it only happens when a fixture is on, using the stop valves allows you to isolate shower valves.
Could it also be that the water heater is working fine, and the problem is with the mixing valve in the shower?
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I don't think there are any shut offs. They are Delta valves and I saw no screw adjustment from the front when I was swapping cartridges. There are shut offs for the sinks and toilets but no access to tubs and shower.
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OK, try this: shut off the hot water. Open the valve in the shower so cold water runs out. Go to a sink and open the hot faucet. Do you get anything? Try that with each shower, one at a time. Then look at every fixture in the house that mixes hot and cold, and check them too — washing machine, tubs, etc.
Are your shower valves thermostatic? I find they tend to be more troublesome.
What you want to be thinking about is diagnosing the problem, which starts with getting a grasp on the symptoms. Keep a thermometer by the sink in your shower. Measure your hot and cold water temperatures at the sink to get a feel for what normal temperatures look like. When the shower starts acting up, leave the shower running, go to the sink and measure the temperatures. That might give you a glimpse of what's going on.
At this point the question is whether it's just the shower mixing valve acting up, or the whole hot water system.
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Your suggestion is similar to the test in the manual I posted back a few posts.
Turn off the hot water and open all the hot water valves in the house. Check them in 10 minutes. Any continued drips large or small indicates a plumbing crossover.
My results are only the 3 master shower valves all continue to drip. Every other valve stopped dripping in seconds.
So where do I go from here? No plumber so far has been able to definitely tell me what is wrong. I can predict how that's going to play out. "Which valve do you want me to replace" eenie meenie miney moe
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I doubt that the valves are thermostatic my builder was cheap. Gave the illusion of high quality but the subs were horrible.
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I finally wrapped my head around your suggestion. I get slightly different results from the 2 times I tried it.
1st time I shut off the intake valve and checked the 3 valves in the master shower. The over head shower seamed to keep running with just the cold water on. The other two seemed to be 98% off. Went and checked bathroom 3 and it was off both hot and cold. Bathroom 2 the cold seemed to keep running, near normal flow. Went back to check the master shower and now all 3 are only dripping heavily, maybe a gallon a minute? Back to bathroom 3 it still seems to have normal cold water, no hot.
Then I remembered that the kitchen and laundry room sinks are mixing valves. So shut off the intake water again. Now all mixing valves all have only drips. I suspect that the two sinks and baths 2&3 would stop dripping completely within a minute or so. The master shower will continue to drip heavily for an indefinite amount of time.
I'm not sure if the order which I opened the valves in some way changes the results of the test.
Surely someone has experience with this kind of issue.
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Update; Still no clear direction what is causing this. I was talking to another homeowner they are having the exact same issue and it just started a couple of months ago. The same luke warm water at a secondary bathroom that turns cool to cold in seconds. Turn it off then back on you get hot water for seconds then it turns cold.
His plumber replaced 4of4 cartridges it worked for a day and then turned back the same. His plumber is now suggesting that rocks or other debris got into the line and is now restricting the hot water for that valve.
This could turn into a huge expense trying to find a supposed obstruction.
Our house maybe theirs as well, at different times of the day the problem is more manageable. I take evening showers and 3 of 3 around 7 pm were fine. In the morning it's different. I can only theorize about it. If I turn on the hot water at the bathroom sink just let it run. The temperature is like 60% hot and seemingly doesn't change. After letting it run for a couple of minutes turn it off and wait a couple minutes more. Then turn on the hot water at the tub now the water is 90% hot but cools to 80% and stays that way for long enough to take a shower.
If I have to I can live with this I can tell my guests to run the sink hot then wait a few minutes and get a shower. Who would have thought new houses costing between $600,000 - $800,000 would have to jump through hoops to get hot water.
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Hi, @hot_rod mentioned "thermostatic mixing valve" earlier in this thread. Does your system have one? I've had to deal with strange problems like what you're describing because the wrong TMV was installed and didn't play nice with the recirc system.
Yours, Larry
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I believe I said I doubt it. The builder was cheap. We have all Delta fixtures but nothing fancy.
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Is there a way to return the programing to factory defaults? I would check the flow sensor and make sure it is functioning properly. Might try cutting power (unplugging it) to it for several hours.
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Some of the cold water sandwich you are experiencing could be explained simply by the operation of the unit, it is circulating hot water through your piping, but the unit is off, you open a fixture which allows flow through the unit of cold water, the water at the faucet is from the recirc so its still warm, now you get a blast of cold because the unit took a bit to respond (there will always be water going through that is cold when the unit has been off). You turn this fixture off, go to the next, same results, leave that one on, go to next fixture, cold water sandwich and then you get warm water. Changing the flow through the unit can cause the cold water sandwich, having one fixture on first will start the water heater, so the next fixture will be hotter quicker. You combine all of this with a possibility that your water is hard and scales up the tankless and you have a recipe for inconsistent temps.
The key here in my opinion is that you say you have to run the sink for a while and then run the shower to get hot water. I had to do this for about 10 years owning a tankless and nothing was wrong with it, my plumbing just took a while to get hot water, and then coupled with the time it takes for the unit to fire, it feels like it takes forever standing there waiting. Swapped to a tank and problem is solved.
I am going to go out on a limb here and say for 600k you paid for the new house, that you want the water to be between warm-hot when you open the fixture? Save yourself time and hassle, install a nice tank unit in there with a recirc pump (might not even need that really). You can try to save money by having the bozos in there changing parts and not accomplishing anything, or you can just spend some money on a tank and move on to the next headache of homeownership
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This type of issue can make you pull your hair out.
@Ghost_Rider357 It sure seems like a cross-connection is raising havoc in your home, and so far you are on the right track.
Anywhere that there is a single handle type faucet, there can be a chance of cross connection. The shower valves are a good start. What may I ask is the manufacturer of these shower valves?
You can look at your washing machine, and outside faucets with hot and cold water piped to them. Faucets that are supposed to have check valves installed on the supplies. Single-handle bath, laundry tub, or kitchen faucets and mixing valves too.
I have even come across wye connectors that are used for garden hoses installed on boiler drains, or outside faucets that back feed the water making a cross-connection.
Look at these things as well.
The process of elimination. It is a one-step-at-a-time thing. Keep going and write down your findings to get a glimpse of what's happening, until you finally find the issue
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Thanks for your suggestion I do have the option to put a standard tank down the road. Not sure if having the recirculating lines will complicate it.
For now I think partly how it was plumbed and perhaps a insufficient recycling pump and or water heater design is at the root of this.
I think the kitchen sink is first and master bathroom is second and the two other bathrooms are 3rd. I base that assumption on the temperature at the faucets.
The test I posted a while back that's in the manual saying to turn off the water intake at the water heater. Then open all the valves. After 10 minutes if any are still leaking large or small indicates a plumbing crossover.
All 3 valves in the master shower keep dripping heavily indefinitely, or so it appears.
The problem is to check any of that requires busting into the walls. I will need a plumber that I trust isn't going to rob me to show me how big of holes he will need. I will carefully remove the drywall hoping to create access panels where needed.
The thing is like I keep saying there's no guarantee that any of that will solve the problem. If I knew it was going to cost thousands and may not be fixed. I could learn to live with it.
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Hi, I'm thinking this is a multi-step process. Step one is to turn off water to the heater and open one hot tap. It should stop running. If it does keep running, is it a good flow or just a drip? If it's a good flow, there is likely a crossover or a plumbing mistake. I would like to see photos of the plumbing around the heater too. I'm not sure that just because the builder is cheap, that you don't have a mixing valve. Some areas require it. You should not need to cut into walls unless there is some certainty that a plumbing mistake happened. Looking at things with an IR camera can help you to see what's going on without digging into the walls also… A pressure imbalance caused by the recirc pump can slowly fill the hot lines with cold water if there is any (even small) path for water to cross over. A drip is not enough to seriously mess with hot water delivery once hot has arrived though… Putting in tank would eliminate the possibility of cold water sandwich and give you faster hot water. These are just the random thoughts of a troubleshooter. 🤠
Yours, Larry
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I can't tell you what to do with your time and money, but a tank will not have this same problem.
99% of the time I deal with tankless water heater issues (in wholesale, sell a ton of these, different brand they all work the same) it is either poor water quality scaling a unit, or the owner simply doesn't like how a tankless works and should have never had one installed. I would put money on the latter in this situation
You can fix the plumbing to be perfect but it won't change that the tankless will always flow cold water through it for 10 seconds to a minute every time a tap is opened and the unit isn't already running. Remember, every time you open the tap and that heater is not already firing, flow sensor detects flow, signals to turn on fan, then gas valve opens, ignition begins, flame is proved, and NOW we are just STARTING to make hot water. During that whole procedure you have cold water headed to your tap. The recirc alleviates this somewhat, however if the unit was ever off when you open the tap, you will end up with a cold water sandwich as you just sent a half gallon or more of cold water through the piping.
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Testing the tankless heater isolated from the house would be my first action. A good large hot water rated hose connected to the hot service port and run to a safe drain. Test all flow rates with the service ball valve as flow control. Starting and stopping timing the time till flame responds and temperature consistency. Test a neighbors good working unit the same way for comparison. Film both. Turbine flow sensors can be tricky. It's either a heater problem or a house plumbing problem or both. It sounds like the heater is suspect and it should be easy to catch in the act. No codes doesn't mean it works correctly and if there's a history of unit failures in your build community the manufacture should want to make it right. If the heater passes all testing you know to focus the investigation on the house. The thing missing here is exactly what was the flaw was of the pre-updated heaters. Check and mixing valve problems haunt cheap heaters and manufactures keep selling unrevised parts denying issues till it's scandalous and lawyers start talking or it goes away cause people give up and replace.
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Builders being cheap and trying to stuff a water heater in a closet somewhere. Manufacturers know their customers and supply the product to them, they want the cheapest thing on the market, the manufacturer will provide it! No amount of problem solving here will eliminate the cold water sandwich though!, not without storage somewhere anyway. Why would a builder put up a bunch of houses for over half a million each with tankless units? they were being cheap!
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Just worked on a project with pex home run style plumbing. 3/8" for lav sinks. No recirc. with tank-less and the wait time is not bad at all. The tendency to oversize pipe with branch style plumbing and low flow fixtures is a problem. Gets worse when it's long uninsulated main runs of galvi put in by Tim the tool man. " Gonn'a put in 1 inch for this single bathroom."
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Larry the drip from all 3 shower heads after the hot water has been shut off combined is probably at least a gallon a minute. It's a continuous flow seemed like it would just continue never slowing down.
Here are a couple of pictures for you guys
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