Lochinvar Knight fire tube high efficiency boiler

nelsnr2010

I have a Lochinvar Knight fire tube high efficiency boiler that runs a hot water radiant heat system. It was installed in July of 2022 and has had yearly service by the installer. This year, right after we had it serviced towards the start of winter, we noticed it was making a loud vibration/rattling sound while running. Not all the time, but often enough to know something is wrong. We have had techs out seven times now and no one has been able to figure out what’s going on or what’s causing the loud rattle/vibration. They’ve done several combustion analysis tests, all within parameters. They’ve bumped temperatures and water flow. They did a flush and clean out of the heat exchanger. They found a pump that was pulling amps but not spinning and replaced it… the sound continues. It cycles sometimes where it just constantly makes the noise for short 5-10 second bursts over several minutes, or will be a long drawn out vibration for 40-60 seconds. But it doesn’t happen every time it starts up - only a couple times has it actually gone off when we have service here.

We just cannot pinpoint what it could be and get it resolved. There were no issues before the regular yearly service.

Ironman

“There were no issues before the regular yearly service.”

Then he obviously did something that’s causing the issue.

I’d get the same tech back and have him re-trace his steps one by one until he corrects it.

GroundUp

"Vibration/rattling" can mean a lot of different things to different people. I'd agree with Ironman about having that technician back to go over what they did, but there are not a lot of moving parts in these things and any technician worth their salt should be able to pinpoint it relatively quickly by isolating a certain firing or flow rate. It could be an IFC in a circulator, it could be kettling, it could be a chunk of something wedged in the inducer fan, it could be harmonics from improper combustion or gas piping, the list is pretty long… But typically pretty easily diagnosed by a competent technician on site. Could you maybe share a video of the sound here for us to consider?

nelsnr2010

IMG_0715.zip

Here is a video of the sound. I’m feeling very frustrated because everything we’re told seems to just be placating. ‘You’re going to have maintenance like a yearly $600+ flush and valve replacement’ - even though we were never told that risk upon install - and ‘the higher efficiency you go the more finicky these get’ but they have done everything and it’s still rattling, loud enough to hear and feel throughout the house.

Vinny_5

Type in "foghorn" and "fog horn" in the search query on the top right of the page, and you will see a few Lochinvars with the same issue.

Alan (California Radiant) Forbes

There's a rubber coupling connecting the 2" air intake pipe to the fan. I would loosen the hose clamps and pull the pipe off to inspect for anything that could have been sucked in. Leave it disconnected and see if the sound re-occurs. I once found a small bird in there.

The tech. could also have left a tool behind that got into the workings of the boiler.

GroundUp

There is no video, just audio so I have to ask: is the sound most prevalent at a specific firing rate or fan speed? Or is it random? If anybody told you that you need a $600 annual flush and valve replacement, fire them immediately. They obviously have not done everything or it wouldn't still be rattling. It sounds much like a loose part or debris in the fan or venturi, but when it's actually taking place will be the deciding factor on that. Either way, getting that original "technician" back to undo what he did for free is the proper channel if you can't locate it yourself.

Alan (California Radiant) Forbes

https://forum.heatinghelp.com/discussion/comment/1842193#Comment_1842193

There's video there.

GroundUp

https://forum.heatinghelp.com/discussion/comment/1842202#Comment_1842202

All I get is a black screen. Either way, my response remains the same.