Lochinvar Knight KB 80 banging noises
I cannot figure out why there’s a banging noise in the heat exchanger. I’ve cleaned the heat exchanger, replaced the electronic igniter, changed the circulator pump (Grundfos UPS43-100F) and boiler pump (Grundfos UPS26-99FC), cleaned the drain, removed the CSST gas line, and installed a rigid pipe in its place. I replaced the electronic board two years ago. The banging only occurs when it first starts up. When the DWH calls for heat, it still bangs, heating the boiler water to 175°F for water heat. I’ve noticed that the DWH pump gets very hot, and I’m wondering if that might be a sign it’s about to fail. I’m just stumped as to why it’s making this noise. I’ve had this boiler for almost five years, and it’s been working just fine until now. Any ideas?
Comments
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is the noise hydronic or combustion in nature? does the flame change with the noise looking through the sight glass or listening at the exhaust or looking at the diagnostic dial on the gas meter?
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I would say it's the hydronic. The flame has been consistent from start to finish.
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@thewireman, welcome back! I've merged your duplicate posts into one here to prevent confusion.
Forum Moderator
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Never.
Never done it before.
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That should be the first thing to do. Find someone who is familiar with condensing boilers and trained on combustion analysis. Usually you have to check gas pressure to the boiler and test the operation on minimum and maximum firing rates while measuring the CO2 and O2 levels. The manufacturer will have all the details in the installation manual. This is critical to proper operation of the boiler, neglecting to perform these crucial steps is the most common cause of problems with noise and boiler malfunction with high efficiency condensing boilers.
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Ok. Thank you for your help. I'll look into this.
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Combustion analysis first. Are you sure this problem only just started? you had stated all the fixes you attempted and one of those you said was 2 years ago? You've got an absolute ton of pump installed on a very small close tee setup, I don't see how that can really handle the GPM you are pumping through it, I don't think the 43-100 comes with a check valve either so if the flow bleeds through to the other side of the close tees you might have pumps fighting each other. quite possibly the pumps are affecting the other side of the system messing with the flow through the boiler heat exchanger. there also appear to be a couple of leaks and no air separation, we can't see where the expansion tank is located either. If you have leaks, you have air entering the system, if you have an open fill valve attached you are also adding fresh water and oxygen through that. The transition to unsupported pex pipe flopping around attached via sharkbites is also really concerning.
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First of all, it is DIY installed, followed the installation instructions along with a friend who had the experiences with boilers but unfortunately he's no longer around. I only changed the computer board two years ago since it wouldn't turn on at all and that fixed the problem. Before this boiler, or before I bought the house, it had nonworking old school boiler that was connected to old some 2", some 3" cast pipes that is connected to 4 cast radiators up stairs, (2 two story house), 6 cast radiators on the main floor, and that's the reason why I'm using the 43-100. I agree about the pex, and that should be replaced with copper. I don't understand that it has been running just fine for almost 3-4 years, and its starts doing banging.
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O2-5.3%
CO2- 8.9%
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Is that at minimum or maximum firing rate?
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max
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Is this natural or LP gas?
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.0 -
natural
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@ thewireman, sez—"I've cleaned it every year with brush wheel (plastic wire one). "
Look, I've cleaned many of these Knights and it takes more than the plastic wire brush wheel to do the job. You have to clean between the heat exchanger coils. Some use a feeler gauge or a tool to get between the coils. You can get the surface of the HX gleaming clean and still have a combustion build-up between the coils impeding the flow of combustion gasses out of the boiler. Do a good water flushing afterwards.
If you don't have good flow thru the HX, you can get flashing in the HX which can be noisy.
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I don’t see an air purger, just the compression tank fitting. Air in some of the boiler HX coils will cause flashing to steam and banging
The red Grundfos pump needs to run whenever the boiler is firing, it looks to be the boiler loop pump?
If just the green pump runs, you may not be getting enough flow. I think a 35 delta is maximum across the boiler.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Yup, I do clean between the heat exchanger coils. I just cleaned it again, I took pictures of it just in case if you see something funny in there. Check it out-
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I do not have the aftermarket air purger, just the air purger on the boiler's heat exchanger. The Red pump (system circulator) turns on when the thermostat calls for heat, also the boiler circulator turns on. The green pump only turns on when the DHW calls for heat. I have no problem getting hot water and heating for the house, just the noises. And of course, I bled the radiators, as always, not getting air.
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The discolored coils in the middle of the heat exchanger suggest that they’re overheating because you’re not getting proper flow through them.
There could be a blockage on the water side and/or the boiler needs descaling.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.0 -
The air vent on the boiler is not really an air purger, it catches air trapped in the coils to some extent. It's called a high point vent
You could manually purge all the circuits but that allows fresh water in which has air in it.
It really should have a central air purger to catch air that comes out of solution every time the water temperature increases.
Those coil type boilers are tougher to purge, on occasion I have opened the relief valve on the boiler to get some air out.
A pop or banging noise may indicate air is in some of the boiler coils, or a limescale build up inside the coils prevent good heat transfer. You might run a hydronic cleaner to clean the inside of those coils.
You are sure the primary pump is actually spinning, not stuck?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream2 -
Close, but no cigar. You should remove the back refactory when cleaning. This is a pic of a boiler that I clean every three years which is what I find is the max time between cleaning. I don't use the nylon abrasive wheel that is advertised. I use a stainless steel wire wheels which I get from Harbor Freight tools and a rotary tool. I, also, use CLR lime remover and spray the HX while cleaning.
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