Lochinvar boiler / Knight domestic hot water - intermittent loud banging

aksteveex

Somewhat similar to the problem posed by nikibooks this past January (most recent post March 2), we hear a loud singular banging sound that may happen frequently or infrequently on any day. Original installer who has also performed regular maintenance (system about 6 - 8 years old) has been here to troubleshoot. It didn't make noise then, but he heard it on a short video I managed to get lucky.

He released some air (valve on top of main unit, I believe) and poked around, but I don't know everything he did. Noise did not occur while he was here, although we tried to force it by turning up heat in each of the 3 zones. Noise continued after he left, so a few days later by text he suggested I turn down the pump (associated with domestic hot water) from hi to low (3 to 1). Two days since I did that, there does seem to be an overall reduction in frequency of the noise, but it's hard to say for sure. I've heard it twice in a few hours today, which is less than I typically would hear it for the amount of time I've been in close enough proximity to do so.

In the nikibooks thread, someone mentioned possible blocked vent. Our 4" (outside measure) white plastic vent goes out the side of the house and easy to access. Following what looked like normal exhaust, I looked inside with a flashlight and did not see any blockages. I did see some moisture along the inside of the pipe and a small drip outside. I presume that is normal. It's on the north side of the house so no direct sun, I live in southcentral Alaska, it's a nice day in upper 20sF right now.

Unless the opportunity to post pics comes up when I hit "post discussion", I don't see how to do so. Other than that, I'm wondering if someone might have suggestions about this "banging" issue. Thanks.

Ironman

I could be delayed ignition. You didn't give the model number, but if it's one that has the Giononni heat exchanger, then PROPER cleaning and maintenance is essential. Has the HX been cleaned and combustion numbers checked in accordance with the service manual?

Dave H_2

Do you have zone valves on this system?
My guess may be from when you have all three zones open, and then maybe two close or going from 1 large zone and 1 small zone calling from heat and the large zone closes.

Dave H.

aksteveex

I'll ask my installer / service guy about those two comments and any others that come in. Thanks!

aksteveex

Yes, we have zone valves, so that may apply. If so, are you suggesting we may need to replace one or more of them?

Ironman

aksteveex said:

I'll ask my installer / service guy about those two comments and any others that come in. Thanks!

Notice carefully what I emphasized: PROPER cleaning and IN ACCORDANCE with the service manual.

I don't know a thing about your installer or service tech, but experience has proved the vast majority are clueless.

aksteveex

Ironman, thanks for making sure I understood your point. My boiler is Lochinvar Knight WBN 106, (105,000btu). It was purchased and installed September 2010. You may or may not need any of the following to offer me advice, but here's what else I've done and learned tonight:

I removed the cover, but could not determine who made the heat exchanger (I could have missed that). I also pulled out the manuals, etc. stored inside the cover; according to the "replacement parts list" for the boiler, the heat exchanger assembly was at the time part no. HEX 3691 for model WB 106. A search of Lochinvar's website led to what's apparently an updated part number for the heat exchanger: 100147632.

The service manual also refers to "heat exchanger cleaning kit" number KIT30062. The service manual "maintenance and annual startup" page with "service and maintenance schedules" says under "annual start-up" to "clean heat exchanger if flue temperature is more than 54˚ F above return water temperature".

Also on that service/maintenance schedule under "if combustion or performance indicate need"... "clean heat exchanger".

Probably not relevant, but that "if combustion or performance indicate need" section also states: "remove and clean burner using only compressed air", and "clean the blower wheel".

Does any of this tell you anything about if or what type of service should be done on my heat exchanger? I don't know whether or not any service has been done on the heat exchanger in the six and a half years this unit has been in my home. Thanks again.

Ironman

A WBN has the Gianonni HX which should be cleaned every year.

Find a tech who's knowledgeable about that HX. It's been used by several manufactures, but most (including Lochinvar) have moved toward the fire tube HX.

The burner assembly must be remove (and cleaned) in order to access the HX. A brass wire brush, some CLR, and an old credit card are needed to clean the HX. Use the credit card to get between the sections of the HX. This is the most important step that most miss. Make sure it's rinsed off well with fresh water and that the condensate trap and drain are clear.

Here's a link, but he doesn't show a proper cleaning:

https://youtu.be/J6OBoGBtJ8w

Jamie Hall

On the zone valves -- do they close with the flow, or against? Sometimes a zone valve can make a water hammer if it closes with the flow, as it may get slammed shut. Or a very quick closing valve against the flow may do that. There are ways to solve the problem...

CMadatMe

Check condensate trap.. May also be air coming out of solution