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Navien NPE-210A fan runs on toilet flush

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 I have a Navien NPE-210A tankless water heater. After flushing each year, the fan runs on any cold water draw and has usually stopped after a couple weeks. This time, since I flushed it on April 16th, the fan still runs intermittently on a faucet draw and every time the toilet flushes- the unit doesn't fire. Never had an error message, I changed the internal check valve- no change. Today I am replacing the flow sensor. If that doesn't change things either, then what? Maybe the air vent assembly? Could it be the internal recirc causing this problem? I'm going to try to turn that dip switch off today to see if it makes a difference.

So I changed the flow sensor on Saturday and and also turned off the intelligent preheating but left the internal Recirculation on. There's no leaks I installed everything correctly. Really easy to do. The fan still runs when I flush the toilet but not when a faucet runs. The unit does not fire. I have a plumber coming sometime in the next couple weeks to install the Navicirc valve and an expansion tank I guess while he's here I'll have him call Navien And talk to one of their technical experts because even though I told the guy I installed those parts myself he wouldn't talk to me cause I'm not a licensed plumber. I guess I should have just lied and said I was. And once that is installed I'll turn off the dip switch that I left on for internal recirculation and turn that valve inside the unit from internal to external and hope that solves the problem. I don't know what's causing it and I don't know why it used to go away after a month after flushing but doesn't do it this time. I had my whole house but that wasn't it because it worked fine until I flushed it in April repiped last fall but that wasn't it because the heater worked fine until I flushed it in April. There is an external check valve on the cold water inlet side which one of the so called Navien experts put on the last time I had one out here. Maybe that could be the problem. No one has been able to figure it out for years.

Mad Dog_2

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,840
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    Why should the unit get triggered to start when you flush the toilet? That's not connected to the hot water.

    The real question you did not mention is are you getting hot water?

    Mad Dog_2
  • dko
    dko Member Posts: 644
    edited June 20
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    What's your inlet water pressure PSI

  • hot_rod
    hot_rod Member Posts: 22,483
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    a cross connection in the piping somewhere so H & C are blended, a cold water draw must be causing a flow condition in the tankless?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    IronmanMad Dog_2Zman
  • DCContrarian
    DCContrarian Member Posts: 305
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    In humid places it used to be somewhat common to put a mix valve between hot and cold on the supply for the toilet to keep the tank from sweating. It was called an "anti-sweat valve" or a "tempering valve." The last one I saw was in a house built in 1976, as air conditioning has become more common they've gone out of fashion. But they're still available.

    Is it possible your house has one?

    rick in Alaska
  • RussellUpsomgrubb
    RussellUpsomgrubb Member Posts: 5
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    I had a couple slab leaks over the last couple years so last fall I had my whole house re-piped through the walls and the studs. There was never any issue until I flushed the tankless water heater and that's been the same every year except it used to stop after about a month and this time it hasn't. I believe at this point it's probably the external check valve on the unit. Because of the leak, and I'm on a community well which is across the street and the pump is 450 ft down in the ground so I have that dip switch for the well pump turned off and it was working fine until I flushed it but, when I had changed my sediment filter after the house got repiped, I realized that the lack of sand in the filter was probably due to the leak getting fixed that was under the slab. And it probably was leaking a little bit for a long time. So I think the external check valve likely got filled up with sand over a period of time because I had the original external check valve changed once already and that seemed to fix it so when I have a plumber come over and put the Navicirc valve on and an expansion tank I'll have him change the external check valve.

  • Ironman
    Ironman Member Posts: 7,399
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    As Hot_rod mentioned: it’s probably from a cross connection.

    Modern pressure balanced shower valves have internal check valves to prevent cross flow between hot and cold. If one of those is not sealing, it could be pulling water through there.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    SuperTech
  • RussellUpsomgrubb
    RussellUpsomgrubb Member Posts: 5
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    No I had my house completely repiped lby a master plumber and I was here the whole time. There's no crossover between the cold and hot. Otherwise this wouldn't happen only when the water heater was flushed. It would be happening all the time and it doesn't so that's not it. It's much more likely the external check valve like I said.

  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,250
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    Tanklesses are very flow-sensitve. Can be a real P.I.A. I had a Rinnai that would not fire the burner when the hot was opened on a Lav faucet with a Trough type spout...Mad Dog

  • SuperTech
    SuperTech Member Posts: 2,205
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    I've seen cross connections occur in single handle shower valves. Also in washing machines. Turn off the water to either of those things and see if it still happens.

    Zman
  • ChrisJ
    ChrisJ Member Posts: 15,922
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    My sister's house had two cross connections via two "touchless" faucets that I guess the plumber didn't install checkvalves on. Since the faucets are left in the on position and a solenoid turns it on and off, there's a connection between hot and cold all of the time unless there's checkvalves installed on the lines.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • RussellUpsomgrubb
    RussellUpsomgrubb Member Posts: 5
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    First of all as I've mentioned repeatedly I just had the house repiped by a master plumber. And it's not a crossover between Hot and cold because this problem did not occur after the house repipe it didn't occur and never occurs until I flush the tankless water heater every year. If there was a crossover between hot and cold like some people have continued to suggest then it would be happening all the time not just after the flushing of the unit. Anybody read the whole thing when I post something? I've got him coming this month to put the Navicirc Valve in and I'm going to have him install another external check valve when he puts the expansion tank and that recirculation valve. And then I already know that I have to turn off Dip switches one through three to turn off internal recirculation and there's also a small valve you turn by hand from internal to external. The only other thing it could probably be is The air vent assembly on the internal circulation pump. That's a $15 part that I can put in myself. But it's most likely the external check valve on the cold water inlet on the tankless because I had a small leak for a long time that wasn't even registering on the Digital readout on the water softener. Until last year when suddenly it was 0.2 gallons per minute. So I'm pretty sure the external check valve got filled up with sand. Once I had the house repiped and the leak was gone, the next time I changed the sediment filter there was much less sand in there and it had been getting in there on a regular basis because I think that leak was going on for years. So undoubtedly the external check valve got filled up with sand over time.

  • KC_Jones
    KC_Jones Member Posts: 5,750
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    The crossover everyone is talking about has absolutely positively nothing to do with the actual piping the plumber ran.

    If you have a single handle valve of any kind in the house you have the potential for a cross connection. Or as @ChrisJ said the automatic valves can have issues if not properly installed. To be very, very clear. All the piping can be perfect and you can still have a crossover because it happens inside the valves.

    Flushing the toilet is putting a draw on the hot water, the heater is then sensing flow and turning on, but the draw isn't long enough for it to fire all the way so it shuts off.

    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    Larry WeingartenSuperTechZman
  • Robertw
    Robertw Member Posts: 1
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    Very possible the hydraulic jump of the water due to the quick shut off toilet fill valve Can activate the unit. Not a flow per say but a movement. Does it happen when the washing machine solenoids shut off as well?

  • DCContrarian
    DCContrarian Member Posts: 305
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    The title of the thread is "Navien NPE-210A fan runs on toilet flush." In your original post you write: "the fan still runs intermittently on a faucet draw and every time the toilet flushes."

    You have a device that is triggered by demand for hot water, and devices that use only cold water triggering it. The simplest explanation is that those cold water devices are in fact using some hot water.

    Have you tried this: when you're in a period when flushing the toilet causes the fan to run, turn off the hot water at the water heater. Then flush a toilet. If the problem is being caused by hot water flowing when there is demand for cold water, turning off that valve should prevent hot water from flowing and prevent the problem.

    SuperTech
  • dko
    dko Member Posts: 644
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    Severe water hammer can trick the flow sensor in these tankless units into thinking there was hot water flow. Common problem solved by reducing pressure to a reasonable PSI with a PRV or properly placed arrestors and check valves. Most toilet fill valves are quick closing and cause hammer.

  • JMWHVAC
    JMWHVAC Member Posts: 47
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    I saw tankless start the fan on cold water draw on more than one job. With pex piping there is a little give, so when a valve opens there is more movement in the whole plumbing system than we may think. Just enough movement for the tankless to register flow even tho it may only be a momentary "wiggle". Seems a properly situated check valve could take care of it but I never worried about it as I never saw a case where it happened with every cold water run.

    dko
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,333
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    Has any looked for an anti-sweat valve supplying a toilet?

    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
    Larry Weingartenrick in Alaska
  • RussellUpsomgrubb
    RussellUpsomgrubb Member Posts: 5
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    Well since I replaced the internal check valve and the flow sensor it's quit running the fan when I flush the toilet. However it now seems to be running the fan randomly and sometimes firing randomly. I just got back from getting my mail and the fan was going off in the unit but there's no leaks anywhere I've checked again and again overnight to see if any water was leaking anywhere and I just had the house re-pipe last fall so there's no leaks. The master plumber coming to put the navi Circ valve on is going to also put an expansion tank on a small one and I'm going to turn off the third dip switch which controls internal recirculation and also the hand valve that turns it from internal to external and I believe that's going to sound the problem. The cross connection thing doesn't make any sense because it's only ever done this after it's been flushed on a yearly basis. In the past when I have flushed it it would run for about a month on cold water draws and then it stopped. Now I got it to stop after changing those parts but this problem has only occurred after I flush the heat exchanger and never the rest of the year. It doesn't do it all the time. Only after the unit is flushed on a yearly basis. If there was a crossover it would do it constantly and it does not. I don't know how many times I can say this. If not for the flushing the rest of the year it works fine and it doesn't run the fan.

  • DCContrarian
    DCContrarian Member Posts: 305
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    "If there was a crossover it would do it constantly and it does not. I don't know how many times I can say this."

    So far two reasonable explanations have been put forward: one is crossover between the hot and cold somewhere in the system, the other is water hammer on the cold pipe. Until those two have been eliminated there's not point in looking further at more exotic solutions or firing up the parts cannon and shooting new parts into the water heater. And saying, "I don't think that could happen," or even "I really don't think that could happen" isn't eliminating them. I don't think anyone who has suggested crossover is at all dissuaded by the fact that it's intermittent, crossover problems are sneaky like that.

    There is an easy way to eliminate both of them, if you are in a state where you can reliably get the fan to run on a toilet flush. There is a valve that provides cold water to the water heater. Shut that valve and flush the toilet. Does the fan run? Open the valve. There may or may not be a valve downstream of the water heater so it can be serviced. If not you should install one, it's a good idea. Shut that valve, and flush the toilet again. Does the fan run now?

    If it was water hammer, closing the input valve would keep the fan from running, the water heater is isolated from the water hammer with the valve closed. Closing the valve on the output doesn't isolate it. If it was cross connection, closing the downstream valve will keep the fan from running. Closing the input valve may or may not isolate it, you can get some water motion downstream.

    SuperTechTeemok
  • Teemok
    Teemok Member, Email Confirmation Posts: 570
    edited July 6
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    Edit: Next time, I will read the whole thread before commenting. Please excuse my first erased comments.

    Ok, spit ball idea. Air gets trapped in the hot little buffer tank and it acts as an expansion tank charge. When the toilet drops pressure in the cold line the air in the buffer pushes water backwards enough to spin the turbine for a brief moment.? If the re-pipe is pex the pipes on the hot side can have an elastic nature that acts as an expansion tank would, causing hot water to be push backwards like the air theory above. The cold check would have to have failed. I can't see a toilet flush creating correct direction flow through the flow sensor.

    Water hammer would be from the toilet valve closing not opening.

    The fan can be triggered by the system that keeps the buffer tank hot. Both things can be happening causing the fan to be heard. It doesn't take much to heat the buffer so you might not notice the brief flame and you just hear/catch the post burn fan run cycle.