Navien tankless canít keep up with flow?

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  #1  
Old 10-08-18, 04:31 PM
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Navien tankless canít keep up with flow?

Hi there,

I have a Navien NR-210A tankless water heater which is having an issue.

Gradually over a few weeks it it has been less able to keep up with the demand for hot water. It seems to be related to the volume/flow of water. Scenarios:

If I turn on the hot water tap at the bathroom sink, no issues at all.
If I turn on the hot water tap at the kitchen sink, no issues at all.
If I turn on the bathroom and kitchen sinks at the same time, the water turns cold.
If I turn on just the shower or bathtub, the water is lukewarm at best. If I then turn on the bathroom sink as well, both go cold.
If the furnace kicks in while the lukewarm shower is running, the shower goes cold.

The water to the heater is softened. The heater was manufactured in 2010.

I should also mention, the heater is not showing any error codes.

Any suggestions before I call a plumber?

Thanks.
 

Last edited by RM105; 10-08-18 at 04:33 PM. Reason: Additional info
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  #2  
Old 10-08-18, 09:28 PM
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My first thought is it simply does not have the capacity you need but you make it sound like it used to keep up. My next thought, then, is that it is developing scale or something inside - these heaters are pretty maintenance intensive, have you been servicing it regularly?
 
  #3  
Old 10-09-18, 03:30 AM
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Itís not a capacity issue, as Iíve had it for 8 years with limitless hot water. Itís just the last few weeks itís been having trouble, with no increase in water usage.

I follow the operating manualís maintenance procedures twice a year, and it had a full professional check-up about a year ago.
 
  #4  
Old 10-09-18, 02:19 PM
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The clue, I think, is the furnace kicking on also affects hot water. That would seem to indicate that the flame is low in the heater. It may be enough to heat for one low demand fixture, but anymore than that or any additional gas usage and it drops so low it doesn't effectively heat the water.

If you have a gas stove, try turning all the burners on and see if it's the same effect as the furnace.
 
  #5  
Old 10-09-18, 04:35 PM
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I missed the part about the furnace - that makes me think it's a gas/gas line problem.
 
  #6  
Old 10-09-18, 04:45 PM
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The 210A has a circulation pump in it. Although the OP said furnace..... he may have meant when this unit was in house heating mode the DHW temperature went down. If this is correct then ..... was it providing enough water for heat ?

Many plumbers don't service the Navien units.
 
  #7  
Old 10-09-18, 06:28 PM
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My house only uses gas for the hot water heater and the furnace, so I canít do a stove test.

The ďfurnaceĒ in my previous post is referring to the actual house-heating central air furnace. The hot water and furnace are tied together, so typically if somethingís wrong and thereís no hot water, thereís also no house heat. But in this instance the house is heating comfortably. So thereís enough hot water for the furnace, but not enough for furnace and shower togethe, or even just the shower by itself.

Plumbers who are knowledgeable about Navien units are few and far between around here, and the last time I had to call someone over, he spent almost 4 hours here and on the phone trying to figure things out....
 
  #8  
Old 10-09-18, 06:42 PM
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These units are not maintenance free. They require regular maintenance to keep them running. The last Navien unit I was part of the install, the plumbers specifically install valves to allow for flushing and clean out. Similar to other brands of tankless heaters. You may just have to have the system back flushed and treated for calcium build up.
 
  #9  
Old 10-09-18, 09:24 PM
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Now I'm completely lost. A furnace uses fossil fuel and is hot air.
Does your Navien also supply hot water for a heating coil in an air handler for heat ?
 
  #10  
Old 10-09-18, 09:25 PM
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RM105....ok, now I'm confused a bit...(getting to be my normal state). So, the Navien provides hot water to the central unit to heat the HOUSE? I've never even heard of an on-demand unit being plumbed that way. I see you're in Canada (please update your profile with location info) so maybe it's a more common thing than I realized. Boilers providing domestic hot water (DHW), sure....but DHW heating the home...new to me. Never even seen it on the home improvement shows.

It makes perfect sense that your temp drops when the call for heat is made...I imagine that's a pretty large load.

It just sounds...as Z says...that your overall capacity has dropped which would indicate scale buildup or some other issue with the heat exchanger. If the firing and flame are good and water flow hasn't increased for some reason...that pretty much just leaves the heat transfer capacity as the issue. I looked at the maintenance manual and I notice they mention cleaning solution. I imagine it a mild acid of some sort...though with softened water...seems like that shouldn't be an issue. I thought they often didn't soften the water because it can cause other erosion issues? I guess not?

I'm still thinking it may somehow be gas related. But if thats the only gas appliance you have?

If you meant that the GAS line feeds both furnace and water heater (not hot water to the central heat)....I'd bet the heater is tapped off the line that USED to feed just the furnace?? It's possible that the line to the water heater is just partially blocked and it gets enough for a normal low usage situation, but when the furnace fires, gas flow to the heater is reduced. People don't realize there can be crud in gas lines just like water lines.

Well, hope you find someone qualified and experienced.
 
  #11  
Old 10-10-18, 05:33 AM
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Sorry for confusing everyone!

Yes, my water heater really does supply the furnace. Now by furnace, I simply mean colloquially the contraption that heats the home. Nobody, and I really do mean nobody, of my acquaintance has a fossil fuel furnace any more, as itís considered dirty technology, and is very expensive in comparison. Ours all run off of natural gas or hydro (electricity). Everyone still calls them ďfurnacesĒ though. There is a line which runs directly from my water heater into the ďfurnaceĒ. Unfortunately I canít figure out how to attach photos to a post from my phone, otherwise I could show you....

Now back to the actual issue of the water heater itself - Iíve never done a full system flush with solvent, as there has never even been any build-up on the filter when I clean it, because of the softening. I was told when it was installed that I absolutely had to use softened water because hard water will cause them to fail frequently. I will look into what sort of solvent they recommend.
 
  #12  
Old 10-10-18, 09:49 AM
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Nobody, and I really do mean nobody, of my acquaintance has a fossil fuel furnace any more, as itís considered dirty technology, and is very expensive in comparison. Ours all run off of natural gas or hydro (electricity).

Natural gas is a fossil fuel.
 
  #13  
Old 10-10-18, 09:57 AM
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Fossil fuels are coal, oil and natural gas.

This is still confusing, is there a natural gas line running into your furnace?
 
  #14  
Old 10-10-18, 09:58 AM
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Fair enough, I stand corrected. What I actually meant was the heater fuel used in the old style furnaces, which seemed to me to be what a previous replier was referring to/asking about, as I already mentioned mine ran on natural gas.
 
  #15  
Old 10-10-18, 10:03 AM
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The gas line goes into the hot water heater, and a hot water line runs from that to the furnace/whatever you want to call it. So they work in tandem.
 
  #16  
Old 10-10-18, 03:04 PM
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Does that system work in tandem or in series summer, and winter? Just asking.
Sid
 
  #17  
Old 10-10-18, 03:51 PM
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In winter (heat mode) they always work together to provide the house heat. When I switch to cool mode in the summer the water heater is no longer used for air, and the air conditioner is routed through it (the ďfurnaceĒ) instead.
 
  #18  
Old 10-10-18, 05:29 PM
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If your water heater is heating your house, how do you prevent yourself from being scalded when using the hot water at the tap? At 120 degrees, max for tap water, how can that possibly transfer enough heat to warm the house? Old style boilers, registers used Steam (212 degrees) to heat a house. I think we all are confused now. Isn't this fun.
 
  #19  
Old 10-10-18, 05:53 PM
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The water is set at 130 degrees. I looked up my actual ďfurnaceĒ model on the web and itís officially called a water source air handler. No steam.

The specs on the serial plate say ďHeating capacity @ 3GPM in BTUs, 130F ó> 17,000Ē. I canít explain the hows and whyís of it, but it is definitely capable of heating and cooling my house just as well as a traditional unit, with the outdoor temperatures where I live ranging from -20C to +36C.
 
  #20  
Old 10-10-18, 09:51 PM
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If you're running hot-hot water for heat, and not-quite-as-hot water for domestic use, there may be a tempering valve involved. If so, it may be failing, and that would explain why you have heat but not enough hot water.

Do you have radiators or baseboard heat? It's not common to have one tankless water heater for both heat and domestic hot water. The one time I've seen it, the hot water (for heat) was routed thru a heat exchanger.
 
  #21  
Old 10-11-18, 02:05 AM
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No radiators or baseboard heat. Itís all forced air vents, 100% heated by the same source.

When using just one water source, such as a sink, the water is the expected hot-hot. Itís just when I use two at a time (i.e. two sinks) or one larger water draw (shower) that the water turns lukewarm or cold.
 
  #22  
Old 10-11-18, 08:16 PM
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Now I'm confused. Your furnace does NOT have a gas line running to it, and it does NOT have a burner? Just a hot water line from the tankless water heater and a blower motor?

The tankless water heaters that I'm familiar with don't send cold water when they can't keep up with demand -- they throttle the flow.
 
  #23  
Old 10-12-18, 11:20 AM
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For some info on the air handler, go to https://www.enerzonehvac.com/, from the main menu go to Manuals, then go to AHC series. It has some diagrams and setup info which might explain things. Also if you google the Navien water heater installation manual, there is a diagram in there giving an example of how a water heater could be connected to a water source air handler.
 
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