Navien NPE-210A fan runs on toilet flush

RussellUpsomgrubb

 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.

EBEBRATT-Ed

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?

dko

What's your inlet water pressure PSI

hot_rod

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?

DCContrarian

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?

RussellUpsomgrubb

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

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.

RussellUpsomgrubb

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

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

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.

ChrisJ

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.

RussellUpsomgrubb

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

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.

Robertw

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

https://forum.heatinghelp.com/discussion/comment/1804786#Comment_1804786

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.

dko

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

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.

Zman

The freshly cleaned HX would have less resistance than when it was dirty. This might be making the flow sensor more sensitive.

I do quite a bit of cross-connect troubleshooting in big commercial buildings. One of the hardest parts is convincing the less experienced facility managers that very small issues with a handheld shower head with a shutoff or faulty cartridge are common causes. Most people have trouble visualizing how hot and cold can comingle so easily.

Charlie from wmass

Has any looked for an anti-sweat valve supplying a toilet?

RussellUpsomgrubb

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

"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.

Teemok

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.

cliffmking

I had the same problem. After I flushed my unit the Navien fan would run anytime I used cold water. Everyone wanted to tell me I had a cross connection somewhere in my house. Water hammer is also discussed on this thread as a possible cause. But the problem only began after I flushed my unit. So logic suggests that the problem is in the unit not in my home's plumbing. Navien's technical support would not talk to me because I'm not a licensed plumber. (That is not what I consider acceptable suport.) I called a Navien authorized technician to address the issue, and he spent a good deal of time on the phone with Navien's level 3 support. But nobody had a solution and the problem persisted. We did some diagnostic testing including turning off the hot water outlet valve, which suggests the problem is not crossover. I also turned off the cold water valves very slowly, which minimized the effect of any water hammer. I finally called my brilliant engineer son, who discussed the problem with me. He correctly pointed out that water does not compress, but air does. We were of the opinion that air was trapped somewhere in the unit (likely in the buffer tank) after the flush. I ran my hot water wide open for awhile and let the internal recirculation (previously turned off) run. The result is I'm still getting a little flow across the flow sensor when I use cold water but the problem is much less severe than before and the unit now only occasionally cycles when I use cold water. Presumably I purged most of the air out of the system, but there is still a little left.

I will try and relay this information to Navien, but that might not do any good since their technical assistance does not talk to homeowners. Navien could also solve this problem by changing the programing of the unit to make it less sensitive to minor flows across the flow sensor, but I'm not going to hold my breath waiting for that to happen.

DCContrarian

How about this theory: There is an expansion tank on the hot water side. When no water is being used, the pressure on the hot and cold sides is equal. When cold water is used, the pressure in the cold water pipes drops, and water flows out of the hot water side to equalize the pressure. Because of the expansion tank the water flow is significant. Once the cold flow stops the pressure rebounds, and water flows back into the hot water circuit. The flow sensor on the heater is non-directional, so it senses the water flowing out and back in again and decides that's enough to fire.

clammy

i personally have seen this happen on one or two occasions and both times it was related to a bad fluid master which was causing migration from the combi and causing issues . And yes a lic plumber buddy of mine was baffled as to what was the issue being he had never seen this occur. It ended up being a combination of things including no portable expansion tank and high water pressure over 125 psi which as strange as it seems caused hot water to be feed to the toilet even though it was clearly piped w a cold water line but i gather there was less of a pressure drop through the hot water line then the cold . Again this was quite a while ago and i haven't ran into this issue again since then . You never know what you ll run into each day the best you can do is start fresh narrow down the issue and use a little non rational thinking to sort it out . i would start by isolating the toilet ,start where the issue occurs and fiqure out why . Remember the cause and effect usually do not happen in the same place .

peace and good luck clammy

Teemok

@clammy Politely, I don't follow.

Claim: A bad fluid master causes hot water in the cold line.

Listed conditions with no working logic as to how a toilet fill valve causes hot water in the cold line. A bad check or the need for one seems more likely but I'm interest in the potential logic of the proposed float valve cause.

The OP was not claiming hot was in the cold but that the draw of cold at the toilet causes the tankless to initiate a heat cycle (Fan run) but does not actually heat anything. Had the house re-piped in pex. It initially only did it for a bit after servicing the tankless. (Air in the small factory buffer tank)

I theorized air introduced into the buffer tank during servicing and or the pex pipe elastic wall stretch effectively creates an tiny expansion tank on the hot side. Pressure drops in the cold cause the tankless flow turbine to spin backwards when the elastic forces of air pocket or pipe walls of the hot piping try to equalize by flowing backwards through the thankless inlet for a brief moment. DC had a similar idea, though he started with an imagined hot side expansion tank.

HydroAirJoe_2

Take a look at the install diagram and you will see that they show a check valve on the cold water supply. If you install a check on the cold water supply, you are going to need to install an expansion tank. My older generation NR240A will turn on randomly, most consistently when the irrigation system draws (the pipe that feeds the irrigation system is near the cold water suppoy of the Navien). I have been living with this since 2010 but I really should of taken care of it.

HydroAirJoe_2

https://forum.heatinghelp.com/discussion/comment/1809747#Comment_1809747

One of the selling features of the Navien is that it requires very little flow to trigger the system to fire.