Lots of water hammer when washers are running

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mdk0420

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Hello all. An issue arised after getting my combi boiler fully operational. Whenever the washers are running I they cause a dramatic water hammer effect while they fill up. I'm guessing this is caused when they open and close the valves to fill it with the right temp water. When I say dramatic, I mean the pipe shakes like crazy and my relief valve and backflow preventer start spitting. I have a pressure reducer set to 60 psi. Never had this issue until I ran the hot water through the tankless water heater and got rid of the 50 gal tank heater I used to have. There wasn't any expansion tanks even on the hot water heater, but maybe the volume helped distribute it. There doesn't seem to be anything specific about needing an expansion tank on a tankless water heater however I'm thinking of putting one on it to see if it'll help the issue. Im not getting one off those stupid arrester canisters. They tend to fail over the course of just a couple of months. I want a relatively maintenance free solution.

Do you think the expansion tank will mitigate or solve the issue? Or won't it make any difference?

I can't repeat this issue through the shower or other regular faucets no matter what combination of smacking faucets closed.

This happens to both washers (mine and my tenants, they feed off a separate hot water heater that's also not protected by an expansion tank).

The specific area that gets hit and starts shaking is right at the pressure reducer which is near the entrance of the main to the house.

Any other suggestions? Again looking for mostly maintenance free solution. It looked bad enough that if I wasn't here it would've probably started damaging things. All the pipes are really secured except for the piping that first comes into the house.
 
Sioux Chief make a hammer arrestor that screws onto the faucet for the washer.
 
Here's a video of it and some pictures. It actually gets a lot worst if I leave it. I notice it starts to happen as soon as it goes from pulling one supply of water to the other. It usually starts out with hot water, it supplies it for a while then it closes and supplies cold water. For some reason it doesn't relieve the water hammer even though the washer is pulling water then and draining the excess pressure from shutting the valve... Not even sure if an expansion tank would solve an issue like this if there is no relief while pulling water... It just makes it worst.



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Sioux Chief make a hammer arrestor that screws onto the faucet for the washer.
I've read all about arresters and their failures. They work great until water fills them up from what I hear. It's easy maintenance but too frequent. I don't mind spending the money to fix it for long term.
 
Well it just happened on the kitchen sink too now. So its not isolated to just the washers. My wife was using both hot and cold together and it started doing it. I'm also going to put a check valve on the cold water supply to the boiler. Not only will it help with any backflow spitting but I'm wondering if when theres a differential between the two, it tries to pull from the hot water line and gets some weird fluctuation in there.
 
My pressure was set to around 60-65 PSI. I like that pressure setting... and never caused an issue until now. I found that turning it down to 45 PSI works. But I'm calling this a temporary solution. I'm not exactly sure what changed in the system besides some additional bends and several more feet for the water to flow through. The old setup was it teed off from the main supply, went to the hot water heater and then made a few elbows make its way to the hot water side of the fixtures.

The new style has the tee coming from the main supply a few feet from the original tee. It runs down where it has the feeder line for the boiler side. It also has a 2nd tee that goes to a basement faucet. It then continues through the boiler and the hot water side comes out, which feeds a hot water faucet in the basement before it makes a few turns and eventually goes back to where I cut the hot water line to tie the new system into it. I don't really see what could've changed except for the amount of water available, but water doesn't compress a whole lot so I wouldn't think that a tank would disperse the water hammer enough.

On top of that the tenants water situation has almost no change except for the location of the tee and the supply line to the hot water boiler. Their hot water piping is separate from mine. But we share the same cold line.
 
Thats not a water hammer. Water hammer occurs when a valve closes quickly causing the flow to stop suddenly making a jolt. The hammer arrestors just absorbs the jolt. You have something disrupting your flow causing that vibration. I have seen washer out of alignment in a valve cause a violent shaking like that.
 
Thats not a water hammer. Water hammer occurs when a valve closes quickly causing the flow to stop suddenly making a jolt. The hammer arrestors just absorbs the jolt. You have something disrupting your flow causing that vibration. I have seen washer out of alignment in a valve cause a violent shaking like that.

Weird. Nothing changed on the main line that runs from the wall to those fixtures except for the one tee being capped and a new tee put in a few feet away to supply the boiler. So far it happened with my washer the tenants washer and my sink. I turned the pressure down to 45 psi and I was unable to make it happen again at the lower pressure but I like the pressure set at 60 PSI. Any ideas what I could do to solve the issue?
 
There are several valves installed that the water needs to travel through. They are all quarter turn full port ball valves. There is one on the supply line to the boiler, one before the boiler that has a drain point, one right after the boiler for the hot water supply and one more on the hot water supply line after the basement faucet.
 
So it's not the typical water hammer caused by a fast closing valve.
I assume it's while the HOT water is running? Not necessarily when the cold water only is running?
I believe it's the double check valve assembly that's clattering and causing the water hammering effect.
First off I'm not sure why that backflow preventer is on a tankless water heater feed line. Didn't think that was a code requirement except on heating boilers.
What is the "combi boiler fully operational" you mentioned?
The fact that you have a PRV on your water service would have dictated an expansion tank even on your previous tank type water heater. Not sure why you were not spitting out water out of the old tanks T&P valve, occasionally.
You definitely need an expansion tank. As to whether it would eliminate the clattering/hammering noise is another question. Many times, adding a single check valve down stream of the backflow preventer will stop the clattering of the backflow preventer.
 
So it's not the typical water hammer caused by a fast closing valve.
I assume it's while the HOT water is running? Not necessarily when the cold water only is running?
I believe it's the double check valve assembly that's clattering and causing the water hammering effect.
First off I'm not sure why that backflow preventer is on a tankless water heater feed line. Didn't think that was a code requirement except on heating boilers.
What is the "combi boiler fully operational" you mentioned?
The fact that you have a PRV on your water service would have dictated an expansion tank even on your previous tank type water heater. Not sure why you were not spitting out water out of the old tanks T&P valve, occasionally.
You definitely need an expansion tank. As to whether it would eliminate the clattering/hammering noise is another question. Many times, adding a single check valve down stream of the backflow preventer will stop the clattering of the backflow preventer.

Codes call for the back flow preventer because it can back flow into your drinking water (even though there's a check valve on the boiler too). No codes call for an expansion tank on the tankless water heater but codes did call for it on the tank. It wasn't there when I bought the house a year ago. I knew I was changing to a tankless and didn't bother installing one when I was going to be changing it anyways.

Ive only been able to get it to happen when both are used. The washer can be on hot and when it switches to cold it happens. It also happens vice versa (from what I can feel in the lines and hear). It also happens to my tenants washer who has a completely separate hot water line.
 
Codes call for the back flow preventer because it can back flow into your drinking water (even though there's a check valve on the boiler too). No codes call for an expansion tank on the tankless water heater but codes did call for it on the tank. It wasn't there when I bought the house a year ago. I knew I was changing to a tankless and didn't bother installing one when I was going to be changing it anyways.

Ive only been able to get it to happen when both are used. The washer can be on hot and when it switches to cold it happens. It also happens vice versa (from what I can feel in the lines and hear). It also happens to my tenants washer who has a completely separate hot water line.
I was confused.
Although I saw your mention of a combi boiler, I didn't realize it was a Domestic H.W. /Boiler Heating System by Navien.
So you have a Navien Combi Boiler unit that provides hydronic heating as well as domestic hot water. That's the reason I see a boiler type backflow preventer in the cold water makeup to the system.
I can understand why an expansion tank would not be required on a Tankless domestic water heater but there should be one on the hydronic heating side. In fact while writing this up I researched it on the Navien's web site and they include sample engineering drawings that show expansions tanks on the hydronic side.
In fact they show one that has a Domestic Hot Water recirculation system that includes an expansion tank.( The reason being because they show a check valve upstream on the cold water service which would prevent any type of expansion.)

So back to why the chattering of the check valves. So you have a PRV on the main water service for the entire house, which acts a check valve by preventing expansion back into the water service line.
You have the double check valve in the backflow preventer on the combo Boiler heating system side for make-up water.(preventing expansion of heating water and thereby requiring an expansion tank on the boiler side.
Do you have check valves or backflow preventers any where else? You mentioned, "there's a check valve on the boiler too". Which line is that on?

EDIT: You don't happen to have a Domestic Hot Water recirculation system, do you?
 

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I was confused.
Although I saw your mention of a combi boiler, I didn't realize it was a Domestic H.W. /Boiler Heating System by Navien.
So you have a Navien Combi Boiler unit that provides hydronic heating as well as domestic hot water. That's the reason I see a boiler type backflow preventer in the cold water makeup to the system.
I can understand why an expansion tank would not be required on a Tankless domestic water heater but there should be one on the hydronic heating side. In fact while writing this up I researched it on the Navien's web site and they include sample engineering drawings that show expansions tanks on the hydronic side.
In fact they show one that has a Domestic Hot Water recirculation system that includes an expansion tank.( The reason being because they show a check valve upstream on the cold water service which would prevent any type of expansion.)

So back to why the chattering of the check valves. So you have a PRV on the main water service for the entire house, which acts a check valve by preventing expansion back into the water service line.
You have the double check valve in the backflow preventer on the combo Boiler heating system side for make-up water.(preventing expansion of heating water and thereby requiring an expansion tank on the boiler side.
Do you have check valves or backflow preventers any where else? You mentioned, "there's a check valve on the boiler too". Which line is that on?

EDIT: You don't happen to have a Domestic Hot Water recirculation system, do you?

No recirculation system, yet. The check valve at the boiler is on the heating side (on the auto feed line). There's actually 4 check valves in total lol. One at the boiler itself (it has its own auto feed system) I put in an auto feed as well with a pressure gauge and strainer, but it also has a check valve. Then there's the backflow preventer that has the other 2 check valves. I'm not sure where I should put my check valve. I think having one on the boilers cold water supply would help keep any have pressure or water hammer from resonating from the hot water line back to the cold water supply and into the main for the rest of the house. Its hard to replicate this on a sink but the washer does it every time (except with the pressure lowered). Soon as it switches from one supply to the other, it shakes the pipes and they continue to shake until I close the valves.

I'm going to at least put an expansion tank near my boiler. After some research I realized I actually only need one expansion tank because even the one near my combi will still act as an expansion tank for the other hot water heater because they are connected at some point through the cold water line.

For now I'm going to continue some research, but I'm at least putting in the expansion tank tonight. Once I find out where to put the check valve I'll do that as well. I want one before the back flow preventer, but I feel like I might need one on the boilers cold water supply too. What are your thoughts?
 
Think of my system as the one that you posted except without the recirculating system and an additional hot water heater (but sharing the sams cold water). That's my system right now. My fear of adding a check valve is if I add it before the expansion tank then the expansion tank would relieve the pressure from the system but then trap it on the combi boilers side and can't disperse it back to the rest of the system or relieve itself without the hot water faucets being turned on. If I do the expansion before the check valve then it won't relieve any pressure that the combi boiler creates on the DHW side of things. Should I just do two with one on each side? Or is that a waste of money for an over precaution? It would have to absorb pressure and then the boiler would have to turn on to hear the DHW without any flow which it shouldn't do anyways. And there's always a pressure relief valve to compensate for an emergency like that
 
No recirculation system, yet. The check valve at the boiler is on the heating side (on the auto feed line). There's actually 4 check valves in total lol. One at the boiler itself (it has its own auto feed system) I put in an auto feed as well with a pressure gauge and strainer, but it also has a check valve. Then there's the backflow preventer that has the other 2 check valves. I'm not sure where I should put my check valve. I think having one on the boilers cold water supply would help keep any have pressure or water hammer from resonating from the hot water line back to the cold water supply and into the main for the rest of the house. Its hard to replicate this on a sink but the washer does it every time (except with the pressure lowered). Soon as it switches from one supply to the other, it shakes the pipes and they continue to shake until I close the valves.

I'm going to at least put an expansion tank near my boiler. After some research I realized I actually only need one expansion tank because even the one near my combi will still act as an expansion tank for the other hot water heater because they are connected at some point through the cold water line.

For now I'm going to continue some research, but I'm at least putting in the expansion tank tonight. Once I find out where to put the check valve I'll do that as well. I want one before the back flow preventer, but I feel like I might need one on the boilers cold water supply too. What are your thoughts?
I'm afraid I'm having a problem clearly following your description. to begin with...you say, "There's actually 4 check valves in total lol. One at the boiler itself (it has its own auto feed system) I put in an auto feed as well with a pressure gauge and strainer, but it also has a check valve. Then there's the backflow preventer that has the other 2 check valves." In your picture I see, on the right side of unit, I see the vertical drop to a tee. The run on the tee which continues straight down, then turns left into bottom of unit, must be the domestic C.W., which will be heated and feed the domestic H.W. system.
The branch off that tee, drops to a ball valve,to a Backflow Preventer, to a PRV w/integral low pressure gauge for feeding the boiler system auto makeup water. This must be what you refer to as the auto feed with pressure gauge and strainer and check valve, you put in. But I don't believe I see the strainer or check valve. Not sure what that small item is directly below and connected to the PRV.
II think the only way I can completely follow your descriptions is with a sketch and/or picture clearly showing all these items.
Where is the, "its own auto feed system"? Below the unit?

You say, "I'm going to at least put an expansion tank near my boiler." On what line? Don't you already have an expansion tank on your heating system?
In other words everything you mention I can't be absolutely sure I'm completely following you. And I don't like assuming anything.

An expansion tank is typically not required on the domestic hot water system(without a recirc system) since it would only be subject to heating up when it's flowing. As I believe you eluded to. However, in your case it may very well act as an shock absorber.
I would put the check valve that's typically added downstream of a backflow preventer, to the upstream side, in an effort to stop he shock waves from bouncing back from the double check valve within the backflow preventer.
 
I'm afraid I'm having a problem clearly following your description. to begin with...you say, "There's actually 4 check valves in total lol. One at the boiler itself (it has its own auto feed system) I put in an auto feed as well with a pressure gauge and strainer, but it also has a check valve. Then there's the backflow preventer that has the other 2 check valves." In your picture I see, on the right side of unit, I see the vertical drop to a tee. The run on the tee which continues straight down, then turns left into bottom of unit, must be the domestic C.W., which will be heated and feed the domestic H.W. system.
The branch off that tee, drops to a ball valve,to a Backflow Preventer, to a PRV w/integral low pressure gauge for feeding the boiler system auto makeup water. This must be what you refer to as the auto feed with pressure gauge and strainer and check valve, you put in. But I don't believe I see the strainer or check valve. Not sure what that small item is directly below and connected to the PRV.
II think the only way I can completely follow your descriptions is with a sketch and/or picture clearly showing all these items.
Where is the, "its own auto feed system"? Below the unit?

You say, "I'm going to at least put an expansion tank near my boiler." On what line? Don't you already have an expansion tank on your heating system?
In other words everything you mention I can't be absolutely sure I'm completely following you. And I don't like assuming anything.

An expansion tank is typically not required on the domestic hot water system(without a recirc system) since it would only be subject to heating up when it's flowing. As I believe you eluded to. However, in your case it may very well act as an shock absorber.
I would put the check valve that's typically added downstream of a backflow preventer, to the upstream side, in an effort to stop he shock waves from bouncing back from the double check valve within the backflow preventer.

Sorry I came off a bit confusing. I'll clear up any questions though.

Your seeing the setup spot on. That line that goes down and feeds into the boiler is the cold supply for the DHW. It tees off just after the shutoff valve to the auto feed system for the boiler. The caleffi auto feeder has the guage, its own strainer, a check valve, and it controls the pressure going into the boiler. The boiler also has its own auto feed function that also has a check valve, not sure if it has anything else. For some reason I've seen a lot of systems include a auto feed even when the boiler has its own. I just put one there for safe measure. And the fact that it has its own strainer makes me feel comfortable about whats going into the boiler :)

So to clear that up, there are 4 check valves in that small section of auto feed line. There's the one at the boiler for its own auto feed (because you don't really need a separate auto feed regulator), there's one at the auto feed I bought anyways, then there's the double check valve.

The auto feed line that tees off the cold water supply leads right into the boilers own auto feed. Which is inside the unit itself and is digitally controlled.

I just put the expansion tank in on the cold water line. The addition is in the picture below. Haven't gotten to test it yet. The line never had any expansion tank. It was supposed too but that is how it came when I bought the house. Shoddy work, not my work. You should see the electrical crap I had to deal with and still am lol.

After some additional research it looks like what you mentioned is the way to do it. To properly do it I think I should have two check valves. One on the cold line and one on the hot line. The reason I'm thinking of doing this is because if I put one right where it tees off to go to the BFP, it would serve to protect that BFP surge, but I feel like the surge is being caused by some differential pressures from the hot water and cold water being pulled in different ways. With what I've been seeing, it happens just as the washer stops pulling hot water and switches to the cold water, and vice versa. So when the hot water shuts off suddenly, it creates that "Water Hammer" and surges all the way through the boiler and back to the cold water supply and the line that the cold water starts pulling from, which then starts the violent shaking. That's just my assumption. I thought it made sense lol. But I'm no professional so I don't know all the variables that you plumbers deal with ^_^

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Oh sorry about the expansion tank not being secured yet lol. I don't feel that it's heavy enough to cause any problems but in the long haul it will be supported lol. I don't have any more of the brackets though. Going to get them tomorrow.
 
So the first test went pretty well. I think the expansion tank did what I was hoping, by absorbing part of the initial impact. My pressure gauge did spike to almost 100 PSI though. Is that pretty normal for water hammering? I figure it'll spike at least a little bit. Better then when it was making my relief valves spit though lol. I still believe check valves would help. I don't mind spending the money on two good spring loaded check valves for both the cold and hot water line. Just don't want it to cause any issues (but I don't see how it could)
 
I've done test after test and I trusted it enough to watch the pressure gauge and I can't get it to surge to more then 75 PSI. No violent shaking still. Not sure where the just under 100 PSI came from. I had my wife turn on and off faucets fast and randomly, and it bounces around from 50-75 PSI. Again, no violent shaking or water hammering. Maybe it did the trick. I guess time will tell. I'm also going to secure the section of water main that comes into the home. That way if it happens to do that violent shaking again, it'll be more stable and won't clatter around the joist and the other pipe that it goes over top. I'll feel much safer knowing that my pipes are breaking each other and I'll be able to tell the after effects by looking for any drops out of the relief valves and my gauge lol.
 
Start back at square one with expansion tanks. Did you calibrate each tank to each system? Each one needs 2psi less than the pressure for that zone of plumbing. Every check valve creates a zone. So you have accurately check each side before tank can be considered to operate if correctly.The water bounces off check then tries to absorb off expansion tank. If that tank pressure is harder than the incoming pressure then your bouncing off that. Or in reverse. Bounce off check and then not enough pressure in expansion. Then tank slowly absorbs the shock just to create even shock wave to open check then you got a chatter box. Check the instructions for calibrating expansion tank to each zone. The boiler side will be less. Or should be. It’s just moving water not pushing like a freight train. I think your experiencing check valve chatter on steroids . Never had it happen on a combi unit but I never installed one. sounds like a well pump that isn’t calibrated with tank and switch.
 

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