Loud thump when it's cold

kevin coppinger_4

yes the wires are a bit of a hazard not to mention a mess, even if they are low voltage...(not good wiring practice)...That boiler is a low mass copper tube boiler. Flow is critical...if only one 3/4" zone calls you could very well have issues w/ banging because the water is flashing to steam in the heat exchanger. You say the this happens at the end of the cycle...I bet that as the zone closes the flow is slowed enough and the boiler is still firing causing the heat to spike and bang...a bypass should have been placed in the boiler piping as per the boiler install manual....looking at the installl we see it was not done...pictures are worth a thousand words...kpc

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pat_23

Loud thump when it's cold

My local boiler guy couldn't figure this out, so I'm hoping the Wall can. Every time it gets single-digit cold here in Colorado, the heating system pipes in my crawl space shake the house with one loud thump each time the boiler shuts down. Thing is, I don't hear it unless it's really cold out. We just replaced two air vents that were broken, which helped for a little while. But now the thumps are back. According to the boiler guy, the next step was a costly purge of the system and other "see if this works" approaches. Any adivce?

Ken_40

Mmmm.

Assuming there are zone valves, they should be located at the end of the zone, not the supply end. It is possible, that wehn both are open, and the ensuing closure of just one of two occurs, the GPM flow is greatest. Closure of one only may induce a pretty hard closing "slam"?

Got a digital camera? Know how to reduce a picture to ~ 800 pixels wide? If so, attach a near boiler pipin photo showing just the boiler supply outlet, the expansion tank tie in point, the circulator(s) and zone valves (if so configured).

We can figure it out.

pat_23

Here are the pictures

There are three zone control valves to the left of the boiler. The one in the back is the one that controls the pipes that make the big bang. Please let me know if these photos work to diagnose the problem

(And while we're at it, are those dangling wires a hazard? The electrician who rewired the house and two boiler guys have told us not to worry about them, but...)

Thanks so much.

pat_23

Bypass

Thanks, Kevin. In investigating what you suggested, I found this dire warning in a low mass boiler manual:

"The bypass arrangement shown protects the boiler from damage caused by condensate corrosion due to low return water temperature. Failure to prevent low water temperature in the boiler could cause corrosion of the boiler sections or burners, resulting in severe personal injury, death or substantial property damage."

Since you note that you don't see a bypass system, is the "big bang" the only thing I need to worry about? Do I need to get a bypass installed right away?

kevin coppinger_4

well..

it should be done...sooner rather than later.How old is the boiler....looks like it has seen better days...get someone who is familiar w/ this set up. kpc

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flanger

We had that problem

> Thanks, Kevin. In investigating what you

> suggested, I found this dire warning in a low

> mass boiler manual:

>

> "The bypass arrangement

> shown protects the boiler from damage caused by

> condensate corrosion due to low return water

> temperature. Failure to prevent low water

> temperature in the boiler could cause corrosion

> of the boiler sections or burners,

> _b__i_resulting in severe personal injury, death

> or substantial property damage."_/i__/b_

>

> Since

> you note that you don't see a bypass system, is

> the "big bang" the only thing I need to worry

> about? Do I need to get a bypass installed right

> away?

flanger

I had that problem

I also live in CO and had that same problem. We also had a copper fin boiler (with radiant floor heating), and it turned out that the bypass was actually corroded shut and after further inspection the entire boiler was full of corrosion (it was only about 10 years old). Unfortunately, we needed to replace the boiler (cast-iron this time) which is very expensive. Also, the installer seperated the boiler side from the radiant-floor tubing side with a heat exchanger. It seems that the 25 yo tubing had become O2 permeable at this age. The good news is that 7 years later, the boiler still runs like it was brand new.

Paul B._2

Banging at the end of the cycle

Hi Pat,

You have a Laars (we haven't been associated with Teledyne for about 10 years now) Mini Therm boiler. It has the "mushroom" type draft diverter, so it's at least 18 to 20 years old. If you have a serial number I can look it up for you.

From the photo's it looks like you have three zone feeds, (with the zone valves on the supply) and only two returns coming back. One of the zones may be 3/4" pipe, it's difficult to tell.

Banging, or knocking with a copper fin boiler, is often caused by lack of flow, or scaling of the tubes. Basically slow moving water, or a thin layer of water trapped between the tube wall and the scale flashes to steam in the heat exchanger. This can create quite a racket.

Since the noise occurs at the end of the cycle (probably after the pump shuts down) I'm leaning towards scale build up.

You can go to our website, www.laars.com and in our "support" area we maintain a list of service contractors who work on our products. In addition to our listed contractors, Laars will provide service support, via our territory service managers to any local contractor, or anyone listed in this sites "Find a Professional" area.

Please feel free to contact me directly at the factory in Rochester, New Hampshire, with any additional questions you may have. I can be reached at 603-335-6300 x 562.

Sincerely,

Paul Bock, Applications Engineer