Pipe noises after Navien 240 installed

[CoachDOC]

Hi all,

Recently had a hot water tank replaced with a Navien240. Immediately after this, we began hearing dripping noises between the 1st and 2nd floor of the house -- nowhere near where the Navien was installed. It's not actually dripping -- there's no visible water damage. We thought it was thermal expansion of the pipes (CPVC), and two plumbers have been out and agreed.

The installer insists that this thermal expansion is not related to the Navien 240, and calls it a coincidence that the noise started when the tankless system was installed (literally the same day). While that's possible, it's a remarkable coincidence.

Our previous hot water tank had an external recirc pump that was removed to use the Navien internal pump. When I checked last week though, the Navien DIP switches and two-way valve were set for external recirculation. I've changed both to the internal settings, but the noise has persisted. Just today, I turned the recirculation completely off and will wait to see if there is a change over the next day or two.

Any ideas here for what if anything about installing a new tankless system would cause thermal expansion noises to start in our pipes?

 

[Fitter30]

Has anyone checked water pressure? Old heater a tank style? Still have the old recir pump? Brand and model

 

[Sponsor]

 

[Reach4]

1. Where is the WH installed-- 2nd floor, basement?
2. Where does the condensate go?

 

[Bannerman]

Is the dripping noise constant or only occurring periodically?
Is the house equipped with a dedicated recirculation return line or is a cross-over valve utilized so the cold water plumbing will serve as the return line?
Assuming a dedicated return line is utilized, did the prior pump circulate hot water non-stop?

Setting the 2-way valve and DIP switch to 'Internal', will cause the pump to circulate water internally within the WH so as to maintain the temperature within the buffer tank. To cause circulation to flow through the house plumbing loop, the 2-way valve will need to be set to 'External' and the appropriate DIP switch setting utilized.

The Navien internal pump will not necessarily circulate hot water continuously. There is a thermal sensor that will shut off the pump if while using a dedicated return line, the temperature of the returning water exceeds a specific temperature. This will reduce fuel consumption, but the plumbing pipes will cool somewhat while no circulation is occurring. Once circulation is resumed or hot water is consumed and the WH fires, the plumbing will become warmer and will expand again.

There is a Thermal Bypass setting (P.17 - pg 68) that may be activated to allow continuous circulation through an external loop. With constant circulation, the pipes should remain always warm, thereby reducing the frequency of expansion/contraction cycles which may eliminate the sound, if expansion/contraction is actually the cause of the sound.

 

[CoachDOC]

Thanks for the replies! Unfortunately I don't have the old pump to get the brand/model, but the previous heater was a tank.

The heater is in the basement. Condensate pump is directly under the unit, and it pumps the condensate into the sump.

Dripping noise is not constant. But we also can't isolate specific times or events that trigger it to start. The house has a dedicated return line. The prior pump ran all the time.

Thank you for the explanation of the internal vs external recirc. I had the pump in the Navien set off yesterday, but I don't notice a particular change. I'll look at the thermal bypass this morning to see if that will do it. Do you know if there's any reason that the pump in the Navien shouldn't run all day? If I find this fixes the problem, should I look into adding a separate external pump?

 

[WorthFlorida]

If you run a recirculating pump all day it will be like turning the heat up. The warm or hot water circulating in the plumbing will act like radiator dissipating heat into the home. Trying to save cold water going down the drain while waiting for hot water, it will cost energy.

 

[WorthFlorida]

Is the dedicated return line still in use? Was there any check valves installed on the old system? Not seeing the whole picture, it could be possible the drip is the return line draining for some reason when the circulator is off. Though it seems not possible.

What type of pipe supplies the water?

 

[CoachDOC]

Is the dedicated return line still in use? Was there any check valves installed on the old system? Not seeing the whole picture, it could be possible the drip is the return line draining for some reason when the circulator is off. Though it seems not possible.

What type of pipe supplies the water?

Yes. The new tankless system uses the dedicated return line. I don't recall any check valves on the old system and don't see any on the new one. Piping is all CPVC . . . for the cold water into the heater and for hot and cold supply throughout the house.

I see in the manual that the Navien should use an external recirc pump if the recirculation pipe exceeds 100ft of 1/2" piping. With the heater in the basement and the farthest faucet on the 2nd floor . . . I think we could be up against or past that limit.

 

[DIYorBust]

It sounds like there may be air in the recirculation loop. Is there a point where you can open a spiggot near the water heater return and run water through the loop to purge it?

 

[Bannerman]

Pipes expand and contract in relation to the amount of temperature fluctuation occuring. Plastic piping will expand and contract at a greater rate than metal piping, but even a tiny amount of movement will ofen cause the sounds you are hearing, particularly where pipes pass through a wall stud or are in contact with other building members. Movement is not always continuous but will usually occur in small steps, with the resulting sound amplified through building components, which is compounded where there are multiple points of contact.

Your previous pump circulating hot water continuously, likely resulted in the plastic pipes to remain in an expanded state, so there was little further movement occuring. With the Navien configured to circulate only periodically, the pipes will then undergo frequent expansion/contraction.

I expect there will be no issue for the built-in pump to operate 24/7. The recommended 100' distance limit is with regards to 1/2" piping for the entire distance. I anticipate at least some of your home's piping will be 3/4" or larger.

Your NPE-240A acheives 96% thermal efficiency by utilizing incoming cold water to extract additional low grade heat from the combustion gases passing through the secondary heat exchanger. If recirculation was to run continuously, that warm return water will be the only water entering the unit. Depending on the temperature, it may be too warm to efficiently extract that additional heat, which will result in lower efficiency while maintaining the recirculation loop temperature during periods of no hot water use.

Instead of continuous circulation, perhaps a good compromise would be to operate circulation only during periods when hot water use is anticipated. Recirculation could commence ~30-minutes prior to rising for work/school, and shut down again after departure. Expansion would then occur before rising, and contraction would occur after departure, so no one will be present to hear the sounds.

Although you may continue to occasionally hear the sounds even as no recirculation is occuring, I suspect the sound is present for sometime following any hot water use.

 

[CoachDOC]

Pipes expand and contract in relation to the amount of temperature fluctuation occuring. Plastic piping will expand and contract at a greater rate than metal piping, but even a tiny amount of movement will ofen cause the sounds you are hearing, particularly where pipes pass through a wall stud or are in contact with other building members.

That all makes sense, and I hope we'll find a solution. The noises appear to be coming from above the kitchen where I know the water lines run through multiple joists. The noise is irritating to be sure, but I also worry about mechanical strain on the pipes as they rub against joists/hangers, etc.

Right now, I have the pump set to run 24/7. If the problem is fixed, then at least we'll have a decent diagnosis and I can start working on a program like you suggest to stop recirc during low- or no-use times.

Appreciate your detailed responses.

 

[Fitter30]

Can view gpm thought the heater and can check it for the return line using hot button.

 

[CoachDOC]

So DIP switches and internal valve are both set to external recirc. And I set the thermal bypass valve to OFF. The dripping sound from our pipes completely stopped.

However, it now takes a long time (30 seconds or so) for our water on the top floor to get hot. And the return line right at the Navien is never hot. So it seems that rather than the recirc pump running 24/7, it now never runs. However, we also don't get these drip noises even when we run hot water upstairs . . . which I would think would lead to some expansion.

I may reach out to Navien directly for some technical support. But in any event, we're in a better situation now that these noises have stopped. A brief wait for hot water upstairs is a minor tradeoff.

 

[Jddery]

That all makes sense, and I hope we'll find a solution. The noises appear to be coming from above the kitchen where I know the water lines run through multiple joists. The noise is irritating to be sure, but I also worry about mechanical strain on the pipes as they rub against joists/hangers, etc.

Right now, I have the pump set to run 24/7. If the problem is fixed, then at least we'll have a decent diagnosis and I can start working on a program like you suggest to stop recirc during low- or no-use times.

Appreciate your detailed responses.

Did turning the pump on 24/7 solve the problem? I think I have the same issue. It's sounds sort of like water dropping on tin, but more hollow lol? Did you find any solutions to this sound?

 

[Jddery]

So DIP switches and internal valve are both set to external recirc. And I set the thermal bypass valve to OFF. The dripping sound from our pipes completely stopped.

However, it now takes a long time (30 seconds or so) for our water on the top floor to get hot. And the return line right at the Navien is never hot. So it seems that rather than the recirc pump running 24/7, it now never runs. However, we also don't get these drip noises even when we run hot water upstairs . . . which I would think would lead to some expansion.

I may reach out to Navien directly for some technical support. But in any event, we're in a better situation now that these noises have stopped. A brief wait for hot water upstairs is a minor tradeoff.

Sorry I see that turning off the recirc pump did solve the problem? What did technical service come back with as a solution? I agree waiting 30 seconds for hot water is a good trade off from hearing that dripping sound, but its sure nice having that hot water there in like 2 seconds haha I guess I can't have my cake and eat it to