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Tankless/On-Demand Hot Water Heater - have one or know anything about gas?

post #1 of 19
Thread Starter 

We put our money where our mouths were a couple of years ago and invested in a gas-powered tankless hot-water heater (a Navien, if that means anything to you).  But it has never worked quite right.  It takes a long time to get warm water, and even then, the temperature varies uncomfortably and sometimes it has an "ignition error" and turns off completely.  Sucks if you're just getting ready to have a shower, sucks even more mid-shower.  irked.gif


It produces a slight gas odour outside, and occasionally we get a faint whiff inside when there's been an ignition error.  Unfortunately, it exhausts right by the only open play area is in our complex, so all the kids play in the driveways.  The gas company has come and measured it, and it's putting out over 500 ppm of carbon monoxide (the safe upper limit is 200).  Not a huge issue outside, but they said it should be fixed as soon as possible 


Installer came by soon after, and said there was a piece of plastic film (like part of a CD shrink-wrapper) partially blocking the air intake, so he put an elbow on the intake so anything that sticks to it once will fall off, rather than stay there.  But I'm sure he was spouting baloney; he also said the "danger" notice from the gas company was garbage and that all the tankless hot water heaters put out 5-600 ppm of CO. 


The latest gas company guy who came by said that he thought maybe we weren't getting enough gas pressure to the water heater (they take much higher gas pressure than traditional water heaters and furnaces), and that it probably should never have been installed without upgrading the gas inputs (then baffled me with lingo and numbers).  And changing the setup also affects the other 2 adjacent townhouses that are part of that input system.  (Can you see the dollar signs piling up?) 


We were also told last year, when the installing company first came out to investigate, that the location is less than ideal because it's right behind where the dryer is, and the venting goes right by it, and the lint gets into the air intake and may be affecting the little burner part (we had that part replaced under warrantee).  Yet another reason why it probably shouldn't have been installed there. 


Other friends have suggested that the new forced air furnace (located in the same utility closet, with louvered closet doors) could be "sucking up all the air", so that a negative pressure is created in the room, and the hot water heater isn't getting enough air.


Would love to talk to anyone here who either has such a hot water heater or knows something about gas (pressure, pipes, that stuff) - I need to know more about this!!!  I'm starting to get hopmad.gif  Stupid finicky new-fangled things!

post #2 of 19

Hmm, I think both the water heater and the furnace should be taking outside air for combustion, not inside air! Our gas furnace has air intake and exhaust pipes outside.


The 8-hour exposure limit for CO is 35 ppm. At 200 ppm, you'd want to evacuate. If you're really getting 500 ppm CO from your water heater, you've got a very serious problem.






post #3 of 19

We have on.  It has been loads of problems.  BOSCH has been horrible to us.  The repair person told us (off the record) that he would never advise anyone to get a BOSCH.  We've had tons of problems but it seems to be (knock on wood) working fine now.


It does take a long time for the hot water to reach the tap but that has more to do with where we put the water heater.  If we did it again we would probably get a couple of smaller heaters and put them in each bathroom and maybe one in the kitchen to help with that.

post #4 of 19
Thread Starter 
Originally Posted by nd_deadhead View Post

Hmm, I think both the water heater and the furnace should be taking outside air for combustion, not inside air! Our gas furnace has air intake and exhaust pipes outside.


The 8-hour exposure limit for CO is 35 ppm. At 200 ppm, you'd want to evacuate. If you're really getting 500 ppm CO from your water heater, you've got a very serious problem.

Thanks for the info about intake air - I'll re-visit the installation manual, but I'm pretty sure it said specifically to use inside air.  The furnace combustion air intake is definitely outside, but it has to take inside air to circulate.


As for the CO, that 500 ppm is right in the exhaust pipe, and it's venting outside, so it's being diluted.  We do leave the basement if we smell any gas smell (because in our case, the CO goes with it).  That's why the gas company guy didn't turn off our gas.  But it definitely needs to be fixed.  I might try contacting the manufacturer. 

post #5 of 19

The problem is that 500 ppm of CO means that your heater is operating very inefficiently - you are not getting complete combustion. The ratio of fuel to air is too high, so you either need to turn up the air or turn down the gas (I don't know if those are adjustments you can make yourself - probably not). The fuel/air ratio could also be the cause of your "ignition error" problems.


This is a very serious issue - that much CO is deadly.


As for it taking a long time to get hot water - it's winter in Canada, and your inlet water temp is probably just above freezing (at least that's how it is in North Dakota). That means it takes a lot more energy to bring the water up to a comfortable shower temp. I have considered a tankless water heater for our house, and what I've learned is that where the winters are cold, you're better off with a combination - a standard tank heater to pre-warm the cold water, and the tankless to make it hot. It's more efficient than a tank because the water temperature is not that much higher than room temp, so you don't have a lot of heat loss.


Good luck, and I truly hope you can get this resolved, for the safety of your family.

post #6 of 19

If you have a sealed combustion furnace, it can't create negative pressure, assuming it is installed properly. "Other friends have suggested that the new forced air furnace (located in the same utility closet, with louvered closet doors) could be "sucking up all the air", so that a negative pressure is created in the room, and the hot water heater isn't getting enough air."


Have you called the manufacturer to find out what the expected exhaust gas composition is? Is it 500 ppm just at the start, or continuously? While you are at it, ask about the minimum gas pressure for the unit.


Did they check the air intake for any other blockages?


How many CO monitors do you have in the house? You should have one for basement, one for first floor, one for 2nd floor, and one for the garage if you have one.


If the installing company has made a mistake by placing the heater so close to the dryer output, you can request that they fix it - possibly by replacing the unit. You would need a well-qualified home inspector OR a different HVAC company to give an opinion on this.


I know it is a huge disappointment for something so costly, but if the unit is not working properly, either fix it or replace it. Maybe the manufacturer would cut you a deal on a new unit if you complained enough?

post #7 of 19

I had to double-check your location because these were the EXACT issues we were having at our old house with the Navien tankless system my landlord put in in May.  It's HORRIBLE!  We also were smelling gas constantly from the pipes that ran outside but the problem was that it vented underneath my kitchen window in the SUMMER so it was cosntantly open and venting back into the house.  Constantly smelling gas.  I mean, STRONG smell.  But we had carbon monoxide detectors in basement, first floor, and 2nd floor and they never alarmed so. . . . .   Also, we had issues with the system shutting itself off.  I mean, it was on and the lights were on but it wasn't working.  We called the installation guy and he checked the error code we were getting and he somehow fixed it.  Don't ask me what he did because I don't know.  But it did keep popping off and on constantly and we'd hav eto go downstairs and unplug it and replug it in again.  Pain in the butt.  And sometimes it was just with no use at all, just overnight.  Also, we still did have the same problem as you that it really took forever to heat up.  My neighbors that shared our duplex had their own Navien system(same model but they had one for their side, and we had one for ours) and they had the EXACT same issues.  I thought the dude who installed them did a hack job and it was cruddy installation that was giving us issues but hearing your story, maybe not.  In trying to figure out the error code myself for our unit, I googled around and found that Navien isn't a GREAT brand and these tankless systems have a ton of issues with them.  Maaybe some googling would help you.  I never figured it out.  We ended up moving for that reason and several others.

post #8 of 19
Thread Starter 

To update a little:

I had the original installation company back in to see if they had any new ideas.  I told him about what was happening, and shared the info the gas company guy gave me.  He took me seriously (unlike the previous guy who was a real toad), and looked carefully at everything.  He decided to extend the intake to the outside (something the first gas company guy had suggested) and to extend the furnace exhaust to the end of the balcony - I hadn't realized they'd only extended the hot water heater exhaust to the end of the balcony and not the furnace one.  The deck is slatted, so exhaust would come up to the deck level - not a big issue with the furnace since we don't use the deck in weather when the furnace would be on, but nice to know he feels the need to get things right.  He didn't have his manometer with him to measure the gas pressure, so he'll do that when he comes back to do the other two.  He also noted that the intake was full of lint again.  So either the previous guy (the toad) didn't actually check (just took the plastic film off and *assumed* that was the problem) or it's really really sensitive.  We haven't used the dryer since the first gas company guy came, so it's just regular household lint.  But now that the intake will be from outside, I'll have to figure something out, because the dryer vents there too!!!  So not sure how that's going to help the dryer lint issue (the dryer vents down near the ground, and the HW heater intake will be about 4-5 feet up from there.)


I've done a bit more Googling - JustMama, if you e-mail me, I can forward you the document I pasted all the info (and links) into.  It could also be that the air temperature makes it harder for the water heater to heat the water to the desired temperature.  It's pretty cool in our basement, and I've overridden the water temp setting to 125 degrees because our main bathroom is 1.5 floors up in the opposite corner.


SleeplessMama - My bad - I actually don't have any CO monitors in the house.  I know, I know, I totally should, and will be getting one the next time I go to a store that has one.  CO sinks, so I'll only keep one in the basement, as that's the only place where CO would be.  (Furnace and Hot Water heater are the only two gas-burning appliances in the house.)


DS says BNH: Backup Nevin Harley.

post #9 of 19

CO does not sink. In fact, CO is slightly lighter than air (a molecular weight of 28, vs 29 for air). And since combustion gases are warmer than room air,they will rise. But because there is air movement in the house, any gas will diffuse pretty quickly in room air, and throughout the house. This is why CO detectors do not specify whether to put them high or low on a wall.


The most important place to put a CO detector (or smoke alarm) is where family members can hear it if they are asleep. If you have a 2-story house, a detector in the basement might go unheard.

post #10 of 19

The air intake may have lint in it from past use of the dryer. Ask them to bring a boroscope and check the entire length of the pipe.

Originally Posted by vancouverlori View Post My bad - I actually don't have any CO monitors in the house. 


You need one per level of the house, plus one for the garage. It is just as important as a car seat for the baby. $25 with free shipping from Amazon, they have many models to choose from. (I am not recommending any specific model.)



I was going to insert the :eek: smiley, but here is something slightly scarier:


more info here:


post #11 of 19
Thread Starter 

Thank you, nd deadhead and SleeplessMommy for the information.  I'll put a bigger rush on the CO monitorS!


Further update:

The original installation company came back to extend the HW heater intake pipe to the outdoors (and to extend the furnace exhaust pipe to the end of the deck.)  This was yet another person to explain the story to.  However, he was very good, took my complaints seriously and was very thorough.  He measured the gas pressure, but said that it appeared to be too high, so he called the gas company in to check it and fix it if needed.  He pointed out that if the pressure was too high, more gas might be going through than the burner can burn, so that could be causing the gas smell and high CO output.  Gas company came, used their more specialized doodads and said the pressure was fine.  (DS, listening from the top of the stairs during this exchange, came to give me "they're arguing" reports every 5 minutes - he was fascinated.)  Installation guy called Navien and spent some time talking to them about the problem.  They said the "board" (by which I think he meant circuit board) could be the problem, but they want him to confirm the gas pressure measurement with a dual port gas pressure measuring thingy, which he didn't have.  So he has to come back to do that (it sounds like the installation company needs to get one in), and if the pressure's fine, then they'll send a replacement board.  He also said that most people with these heaters tend to crank the temperature well beyond the 120 degree limit (I thought I was being brave to increase it to 125!).  I've now got it at 130, so we'll see if that helps in terms of how well it works.  I hesitate to raise it any higher because the surprise bursts of *HOT* water could get dangerous.  As it is, they're pretty darned uncomfortable.


So, we're making progress.  Not sure if it's forwards, but anything is better than where it was at!

post #12 of 19

Did you ever get this taken care of? I was smelling gas outside, not exactly a natural gas smell, but some kind of smell. I called the gas company and the guy figured out it was from the hot water heater, also a Navien. It sounds like the same thing, incomplete combustion is producing smells and carbon monoxide. I am going to get DH to call the installer when he gets home.


I'm wondering if we should have just gotten a regular old water heater.

post #13 of 19
Thread Starter 

We did finally get it sorted out.


We had the gas company come out and upgrade our supply piping to the meter, and the meter itself, then the installers came and completed the job all the way into the house and to the heater.  They realized that our supply lines were not up to current standards (they'd be 25 years old) and we didn't have quite enough gas pressure coming into our unit because they hadn't accounted for the distance of the pipe from the meter to our unit.  That helped a little, but still didn't entirely fix it.


After further discussion with Navien, the installers got a replacement circuit board, but that didn't fix it.  Finally, I pushed, and the installers pushed and Navien, after much avoidance, agreed to replace the circuit board with the latest version - the one that's in the heaters they're currently selling.  That FINALLY fixed it.  All this trouble because the circuit board was a piece of junk to begin with!


So now I've only smelled a faint gassy smell down in the basement if the water heater's been working for a while (like when I have to give 6 cats a bath...), so maybe only once a month.  I can live with that.  The hot water takes a few minutes to get to my bathroom taps (as expected), then there's a slight dip in temperature, then a slight rise, and then it settles down and stays constant.  That is pretty much what you would normally expect with an on-demand water heater, so I'm quite happy.  In fact, it has gotten so good that I haven't even thought about it in months!


So if your Navien isn't behaving, especially if it's more than a year or so old, push the installers to insist that the company supply you with an upgraded circuit board.  Good luck!

post #14 of 19

Wow!  We love our Bosch instant water heater.  It's been running since 2003 and is installed in our kitchen within a custom cabinet and direct vents to the outside.  We never smell anything.  As for the time it takes the water  to heat and get to the outlet being used, that is dependent on the original water temp as it comes from the ground and will be warmer in summer and colder in winter, if you live in a climate like ours (Maine).  Like a pp only thing I may do differently next time is also install some smaller ones a point of use, i.e. each sink, tub, washer.  I guess the only downside for us is that when one of us is shower and another one of us uses the hot water or the washer or dw is running we may get a slight temp change, but it is not often and  can be avoided with planning (pause wash cycles when showering) and consideration for others.  I think it is worth it financially and environmentally.  Would definitely do it again.  Oh, yeah I installed the plumbing in our house including the water heater.  The propane was professionally installed (i'm not crazy!).  It was definitely exciting when I finally turned on the heater the first time....



ETA--Just noticed that my avatar pic shows the cupboard the heater is enclosed in on the right (my left)

post #15 of 19

Our Navien is still giving a gas smell outside. It seems to only smell when it kicks on to recirculate or whatever at 6 pm. I am going to get DH to call installer again. I will mention that circuit board problem to them. I would just like to junk it, I'm worried about the smell outside.

post #16 of 19
Originally Posted by lindberg99 View Post

Our Navien is still giving a gas smell outside. It seems to only smell when it kicks on to recirculate or whatever at 6 pm. I am going to get DH to call installer again. I will mention that circuit board problem to them. I would just like to junk it, I'm worried about the smell outside.

Bummer!  I'm sorry to hear that.  Good luck and I hope that the problem is solved without too much investment.

post #17 of 19

Hello OP,



post #18 of 19

Hello folks...licensed plumber and Navien installer here...


So here's the un bias truth about Naviens.  Some Early models had computer issues.  All your installer needs to do is call a factory rep and they will tell the plumber if the model heater you have had computer issues.


The gas company emplyee's are  a bunch of idiots with hardly any training in actual plumbing or appliances, but are real good at causing a panic by telling people there is a high level of gas coming from outside the exhaust vent.


It is normal to get a moderate to at times heavy smell of gas from a Naviens outdoor exhaust.  Naviens use a modulating flame.  This means the flame can rise and fall very quickly and frequently inside the combustion chamber.  Some times the flame will go out completely if the computer senses the water is being heated too much.  This on and off cycle means that raw gas is sometimes sucked out with exhaust products.  This is normal and does not necassarily mean there is a problem.


Most navien heaters don't have any problems.  I have installed about 30 of them and of those I have had 2 total replacements, and 2 repairs requiring small parts, 2 that just needed intake cleaning.  I have aboutthe same or more amount of failures with normal tank type water heaters.


The problem with many HE water heaters is that the plumber never tells the buyer that like there furnace the water heater will need to be serviced regularly.  This means a trained proffessional looking inside and cleaning the filters (air/water) and looking for problems.  Sometimes after few years of use they need to be de-scaled just like a coffee maker.  The basic rule of thumb is Naviens need 1 fresh air from OUTSIDE for their intake piping, this should be away from clothes dryers and other debris producing house vents. 2 Ample gas supply pressure available at the meter. 3 Proper gas pipe size and location, the Navien should be the first gas appliance from the meter on the gas pipe system.  If this is not possible than gas pipe sizes should be increased. 4 Periodic inspection and if needed cleaning, these are highly advanced computer controled machines.  You wouldn't let your PC get filled with dust and lint and not expect that to be a problem, so why would you think any computer would function that way?


The bottom line is if you want a HE water heater than choose a proffesional who is knowledgeable in that brand and has factory connections that can assist in advanced electronics diognostics and unless they tell you to evacuate your home, don't listen to gas company service techs.  If they really knew what they were talking about the would be plumbers earning twice the pay, not walking around with a gas sniffer for $12.00 an hour. The available gas pressure to your home needs to be high enough and pipe sizes correct.  This should all be checked before the heater gets installed.  On almost every page of the Naviens installation guide there are references to gas pressure requirments and pipe size.




In closing Naviens are only as good as the install and your average quality install for a large Navien in MA is about 3K excluding gas company/federal rebates.  So if some handyman or plumber with a pick up truck installed yours for $2200.00 you should watch out for obvious mistakes and cut corners to save on expenses.


I would also like to echo the posters coments about CO detectors in the home.  This is a must for any home and will help you sleep better at night.  If you don't have CO detectors in your house, get some ASAP.


Best of Luck to all,


Plumber Pete

post #19 of 19

Hi, I am a plumbing contractor living in the SF bay area. Tankless water heaters require more gas to operate than conventional tank type heaters. The amount of gas an appliance needs is expressed in a value known as a BTU (British Thermal Unit). 1000 BTU’s  is equivalent to approximately 1 cubic foot of natural gas. Tankless water heaters range from 120,000 – 250,000 BTU input. A rule of thumb for tank type water heaters is 1000 BTU’s per gallon of storage capacity. That means even a very large domestic tank type water heater of 100 gallon capacity would only require 100,000 BTU’s (actually less than that). What this means to you, is the smallest tankless will always require a larger gas line than your old tank type water heater. It won’t on the other hand require more pressure, just more volume. You get more volume with larger pipe sizes at the same pressure. If your gas line was not upgraded to a larger size you may have problems with the unit and your warranty will definitely be void.

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