Bang, Bang Goes the Hydronic Boiler

planet_queens

Hello, I have questions about how to stop my Laars mini-therm JVT Gas-fired Hot water boiler from banging when it operates. The hydronic system was installed about 10 years ago and consists of two zones of pex lines and baseboards. I posted pictures of the unit to help show the piping and Laars install diagram.

The noise is coming from inside the boiler and begins as the burners fire up. There is a banging and whacking noise and the pressure gage starts to jump up and down between maybe 15 psi to 10 psi. I have purged the two zones many times over the 4 years I’ve owned the house and as soon as thermostat calls the boiler it starts banging again.

The only way I have found to make the racket stop is by calling both zones at the same time and with both circulators going the noise stops. But heating the basement and 1st floor of my house in tandem all winter is not a great solution. As you’ll see the system is not set up to pipe away (two circulators are on the in-flow side) and there is no air scoop or as Laars indicates in their install diagrams there isn’t a by-pass in there either, In fact what the Laars diagrams show and what I see have little in common.

I’ve had four plumbers look at the system over the four years I’ve owned it. The one thing they have agreed on is that the expansion tank is shot and I need a new one (I’ve now annually replaced 3 or 4 expansion tanks) I’ve also been offered air separators as well. Though it is hard to imagine an air separator is going to do it when a freshly purged system still bangs.

Does anyone have experience with these systems and have an approach that has been successful?

Thanks!

Jamie Hall

Does the banging start right away -- or after perhaps a minute or so? What I'm wondering is if you may have relatively low pressure in the boiler, and you are getting localized boiling in there and steam collapsing. That can make quite a bang.

Is there a bypass line? Does in do the same thing if the bypass is open?

nicholas bonham-carter

Were the expansion tanks recharged to your system pressure before having been installed? Without that the tank diaphragm will be pressed against the inner surface of the tank, resulting in no air cushion at all.
There is a lot of dissolved air in any makeup water fed into the system, and so an air scoop is a necessary part of the whole system.
The real clue is the absence of hammering while both zones are heating, and someone else may be able to pinpoint the cause from that.—NBC

Mad Dog_2

You sure it's not over-fired? Mad Dog

hot_rod

A lot of times the noise is due to the copper tubes getting scaled. Called percolation, sounds like an old tea kettle heating up.

If it happened slowly over a period of time this is usually the cause.

Certainly make sure the circulators are operating and you have some pressure in the boiler.

There are de-scaling products available, circulate for a few days and flush out.

Also make sure it is not taking on fresh fill water from a leak in the system somewhere.

planet_queens

Here is a link to video of the boiler firing showing the temperature and pressure gauge. The is an initial percolating sound that happens before the banging begins. The microphone on my camera makes it sound more like a clicking then banging.
https://youtu.be/9XqyZigHxSEhttps://youtu.be/9XqyZigHxSE

planet_queens

Jamie Hall said:

Does the banging start right away -- or after perhaps a minute or so? What I'm wondering is if you may have relatively low pressure in the boiler, and you are getting localized boiling in there and steam collapsing. That can make quite a bang.

Is there a bypass line? Does in do the same thing if the bypass is open?

Jamie,

Thanks for your reply. There is no by-pass on the system. It sounds like it first starts to percolate then bang, I posted video to help illustrate. Also The low pressure cut off has never engaged and the gauge was just replaced so I wouldn't suspect low pressure.

planet_queens

nicholas bonham-carter said:

Were the expansion tanks recharged to your system pressure before having been installed? Without that the tank diaphragm will be pressed against the inner surface of the tank, resulting in no air cushion at all.
There is a lot of dissolved air in any makeup water fed into the system, and so an air scoop is a necessary part of the whole system.
The real clue is the absence of hammering while both zones are heating, and someone else may be able to pinpoint the cause from that.—NBC

@Nicholas,

Thanks for reading over my problem. The lack of air scoop certainly makes me suspicious but wouldn't I at least get a moment of peace and quite right after purging all the air out of the system before boiler went back to banging?

Also the very short zone (less then 1/2 the length of the 1st floor zone) in the basement doesn't bang when it runs alone. There is a completely separate (boiler and all) single zone system that runs the 2nd floor apt and it doesn't bang either.

I think you are right about the "The real clue is the absence of hammering while both zones are heating".

Canucker

It doesn't look like it has P/S piping. If the banging goes away when both zones are calling, I'm guessing without a bypass, it's a flow problem and @Jamie Hall is right.

planet_queens

hot rod said:

A lot of times the noise is due to the copper tubes getting scaled. Called percolation, sounds like an old tea kettle heating up.

If it happened slowly over a period of time this is usually the cause.

Certainly make sure the circulators are operating and you have some pressure in the boiler.

There are de-scaling products available, circulate for a few days and flush out.

Also make sure it is not taking on fresh fill water from a leak in the system somewhere.

@hot rod

It does sound an old tea pot percolating as it works it's way up to banging. I posted this link to youtube where you can hear it go
https://youtu.be/9XqyZigHxSEhttps://youtu.be/9XqyZigHxSE.

The circulators are running and the pressure gauge indicates there is sufficient pressure. I hope there are no leaks I have yet to find soggy sheet rock anywhere and my water meter doesn't indicate any constant water loss.

Are speaking of de-scaling the heat exchanger in the boiler?

Thanks for your thoughts

planet_queens

Canucker said:

It doesn't look like it has P/S piping. If the banging goes away when both zones are calling, I'm guessing without a bypass, it's a flow problem and @Jamie Hall is right.

@Canucker

Thanks for weighing in, what is P/S piping?

Jamie Hall

P/S piping is a method of piping a hot water system in which there is one short "primary" loop which leads from the boiler right back around. It has a pump on it, of course. The idea is to make sure that the boiler always has circulation at enough pressure to keep flash boiling from occurring -- among other things. That's the primary --"P" -- loop. The secondary loops take off from that primary loop and provide flow to the various zones of the heating system -- those are the "S" loops.

In your setup, that short basement zone also ensures that there is enough pressure in the boiler, because it is so short. Or when both zones are calling, there will be more pressure in the boiler. When only one zone is calling, the pressure in the boiler may be just low enough to give localized flash boiling at hot spots.

hot_rod

The manual for the boiler, available online will show the minimum flow it requires, and sometimes pump selection.

A bypass assures you always have adequate flow. Primary secondary piping or a hydro sep will also. I don't see a bypass piping in the pics.

If you do repipe it I prefer a hydraulic seperator to P/S piping as it would give you other important functions like air and dirt elimination.

Has it always made the noise, or is is starting and getting worse?

A bypass with a pressure activated valve PAV or PAB would be ideal if you decide to pipe a bypass, as you dial in the exact bypass flow.

planet_queens

Jamie Hall said:

P/S piping is a method of piping a hot water system in which there is one short "primary" loop which leads from the boiler right back around. It has a pump on it, of course. The idea is to make sure that the boiler always has circulation at enough pressure to keep flash boiling from occurring -- among other things. That's the primary --"P" -- loop. The secondary loops take off from that primary loop and provide flow to the various zones of the heating system -- those are the "S" loops.

In your setup, that short basement zone also ensures that there is enough pressure in the boiler, because it is so short. Or when both zones are calling, there will be more pressure in the boiler. When only one zone is calling, the pressure in the boiler may be just low enough to give localized flash boiling at hot spots.

@Jamie Hall

Thanks for breaking it down for me I think I can visualize your description. it would look like the top diagram - Laars multi-zone valve system I posted.

Is it that the "P" a tight loop and pump keeps enough pressure in the system so that steam is unable to form?

Then is the low pressure you mention is short and momentary as illustrated by the pressure gauge actually dropping below 15 psi in tandem with the banging as steam forms?

EBEBRATT-Ed

You need primary secondary piping with that boiler. I believe that is a copper fin boiler. Constant full flow when firing is mandatory

kcopp

That boiler is VERY sensitive to flow issues. Too little water passing through will give you that issue.
That boiler was never piped properly.
Minimum needs a by- pass. Really should be piped w/ a boiler loop and a system loop. A pump for each.

planet_queens

hot rod said:

The manual for the boiler, available online will show the minimum flow it requires, and sometimes pump selection.

A bypass assures you always have adequate flow. Primary secondary piping or a hydro sep will also. I don't see a bypass piping in the pics.

If you do repipe it I prefer a hydraulic seperator to P/S piping as it would give you other important functions like air and dirt elimination.

Has it always made the noise, or is is starting and getting worse?

A bypass with a pressure activated valve PAV or PAB would be ideal if you decide to pipe a bypass, as you dial in the exact bypass flow.

@hot rod
To answer your question there is no by-pass and the boiler has been banging away since I bought the house 4 yrs ago.

Repiping sounds... awesome. I quickly looked at hydro separators they are not inexpensive but will it successfully serve the roll of a bypass and air separator? Because I don't have either on this system.

hot_rod

Hydraulic separators make it easy for installers that don't know or want to learn primary secondary piping and the finer points to correct P/S piping

If the installer is learning P/S while the meter is running the cost of the hydraulic separator, in your dollars and frustration, will be much lower.

planet_queens

kcopp said:

That boiler is VERY sensitive to flow issues. Too little water passing through will give you that issue.
That boiler was never piped properly.
Minimum needs a by- pass. Really should be piped w/ a boiler loop and a system loop. A pump for each.

@kcopp
I believe you about the never being piped correctly part... RTFM. Should an air scoop or air remover of some sort be added to the system when it is repiped?

As per @Jamie Hall @Canucker @hot rod comments I have a new understanding of the value of a p/s piping which is great. Not that it would have been more useful if the plumber who installed the thing had understood.

Thanks!

kcopp

Air separators are always a good idea. Caleffi has lots of neat stuff to help you w/ this.

hot_rod

Here is some good reading on separation, share it with your installer.

And in a nutshell the graphical difference between the piping of P/S and a hydraulic separator.

Zoning could be a single circulator and zone valves, or multiple circs for the zones. In your case zone valves with a delta P ECM circulator would be sweet.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_15_na.pdf

planet_queens

@hot rod
thanks Bob I will check em out

bart0977

> @planet_queens said:
> Hello, I have questions about how to stop my Laars mini-therm JVT Gas-fired Hot water boiler from banging when it operates. The hydronic system was installed about 10 years ago and consists of two zones of pex lines and baseboards. I posted pictures of the unit to help show the piping and Laars install diagram.
>
> The noise is coming from inside the boiler and begins as the burners fire up. There is a banging and whacking noise and the pressure gage starts to jump up and down between maybe 15 psi to 10 psi. I have purged the two zones many times over the 4 years I’ve owned the house and as soon as thermostat calls the boiler it starts banging again.
>
> The only way I have found to make the racket stop is by calling both zones at the same time and with both circulators going the noise stops. But heating the basement and 1st floor of my house in tandem all winter is not a great solution. As you’ll see the system is not set up to pipe away (two circulators are on the in-flow side) and there is no air scoop or as Laars indicates in their install diagrams there isn’t a by-pass in there either, In fact what the Laars diagrams show and what I see have little in common.
>
> I’ve had four plumbers look at the system over the four years I’ve owned it. The one thing they have agreed on is that the expansion tank is shot and I need a new one (I’ve now annually replaced 3 or 4 expansion tanks) I’ve also been offered air separators as well. Though it is hard to imagine an air separator is going to do it when a freshly purged system still bangs.
>
> Does anyone have experience with these systems and have an approach that has been successful?
>
> Thanks!

bart0977

New member here. My Laars mini therm JVS75 was just replaced under warranty for a failed heat exchanger after only 4 years. It was whistling like crazy! The contractor installed it originally as a “multi zone valve system” as is pictured in the manual. However, the bypass was only a 1/2” copper loop instead of 1-1/4”. I determined (not the contractor) that the delta t was around 50 degrees F, and with 13’ of head, the Taco 007 he put in was grossly underrated and did not have nearly enough flow, and this likely screwed up the heat exchanger. Needless to say the Laars factory would only cover it under warranty if the new install included P/S piping. I also purchased the Taco VT-2218 variable speed circulator to avoid the huge delta t in the future. So the new piping arrangement is “P/S multi zone valve system” as described in the manual. My only concern now, unless I’m missing something, is there’s no way for the 3 minute post pump purge, as the VT-2218 zone pump would have nowhere to move any water. Is there a way to post purge just the boiler circulator (Taco 007)? Will this lack of purge cause another problem in the future? Thanks for any feedback.

Mark Eatherton

The expansion tanks location is causing the boiler pressure to droop below steam flash pressure and BANG, STEAM FLASH. And yes it is typically preceded by the boiling sound. MOVE THE EXPANSION TANK to the boilers outlet, or per the manufacturers drawing so it is as close to the pumps as possible and your problems should go away. Pipe it per their drawing, exactly. They have more experience with their products than anyone.

ME

bart0977

I hope my attached pic works to shed a little light on my post above.

NY_Rob

bart0977 said:

...My only concern now, unless I’m missing something, is there’s no way for the 3 minute post pump purge, as the VT-2218 zone pump would have nowhere to move any water. Is there a way to post purge just the boiler circulator (Taco 007)? Will this lack of purge cause another problem in the future? Thanks for any feedback.

Unless the boiler controller board has an option to control the primary and secondary pumps individually you'll just need to disable the feature or let the secondary pump deadhead for 3 min. Lack of post purge won't harm the boiler, it's there to wring the last bit of heat out of the HX after the fire is out.

Mark Eatherton

Still doesn't look right to me. Boiler pump is pumping towards the expansion tank. Must pump AWAY from the expansion tank. What you have now is better than before, but still not right.

ME

hot_rod

Locating the PONPC on P/S piping can be a challenge. As Mark mentioned you have one pump pumping away, one pumping towards the PONPC.

I'd rather see the tank connection moved to the inlet of the boiler circulator so the boiler itself sees the delta P.

If the secondary circ is closer that 1/2 way around the primary loop, from the tank connection it is pumping away.

HomerJSmith

Bart0977, Minifins have a very low pressure loss thru the HX. Putting your pump on the return to the boiler is essentially pumping into the X-tank. But it is such a short loop with nice large header it probably doesn't make any difference how close the pump is to the X-tank. Nice looking pic tho and you have hydrolic separation between load and supply. It's nice to see clean work.

planet_queens, manually open up the Flo-checks and see it that makes a difference.

Mike_Sheppard

My guess is the boiler has never had the right flow since it was installed. On copper tube boilers flow is important. Without it the heat exchanger can scale. I would suggest having the boiler service and inspect the inside of the heat exchanger. I don’t deal with copper tube boilers very often but I deal with commercial copper tube water heaters almost every day and they start to pop and bang when they get too much scale build up.