Lochinvar Boiler Ignition Resonating Noise

I'm looking for help diagnosing a loud knocking noise that occurs during ignition in my Lochinvar Knight boiler.
This boiler was installed in 2016 and I haven't had any issues or strange sounds until this winter. As it got colder - and therefore use increased - it started making a loud banging sound on startup. The thumping noise vibrates up the wall and into windows in my daughter's bedroom right above - it wakes her up randomly throughout the night.
After lots of reading, and hours of watching/listening, I've narrowed it to the moments around ignition. It seems like the flame is stuttering or popping, creating the sound that carries up through the system. Sometimes it's quick, other times it lasts a full minute.

The sequence I've noticed is: igniter heats, flame begins, flame percentage drops to 25%, loud vibrating rumble begins, flame percentage increases over 30%, flame pops, noise ends.

The folks at Lochinvar will no longer speak with homeowners about diagnostics (I get it, liability). I called a tech recommended on the Lochinvar website who came out and charged me $1,000 to clean the boiler. When he left it still made the sound. For my daughter's sanity, I need to get this fixed, and am capable of doing it myself, with some guidance. I've read about bad natural gas flapper valves, stiffening bars, recalls. Is there a clear "solution" available? Alternately, is there a handy work-around (like setting the flame min to 31%)?

Fire Tube at Startup:
https://youtube.com/shorts/mlJ_DXIlUdI?feature=share

Control Panel at Startup:
https://youtube.com/shorts/tMfbOn80dUw?feature=share

 

Cleaning alone will not resolve the issue although service should have been done every year if not two years. You need to have a qualified technician perform a full combustion analysis along with manometer testing. The noises you are having are most likely related to combustion and air/fuel mixture issues. Without proper equipment and proper knowledge of how to use it and make adjustments there is very little you will be able to do. I'm sorry you got taken for $1000 for a cleaning only.

 

The tech did do an analysis, and said all of the numbers looked good, then left. Here is the printout:

 

E,
I've never worked on a Lochinvar but after looking at your clips, in the first one your fire is modulating all over the place. After a little research it looks like you have settings for a 10:1 modulation and how to properly set it up. That is just my suggestion. As far as the clicking goes that is your ignition kicking on.

Wish I could be more help but honestly without the manual and not being there it's the best I can do.

Hope this helps a little.

 

Thanks Spott. The term modulation helped a lot. I adjusted the ramp settings, yesterday, so the boiler would start at 30%, skipping the 25% startup altogether. It had a great initial result - no loud startup noise. However, it modulated down to 20% for the "post-purge" phase and the same noise occurred for almost two minutes. But I'm onto something.
Interestingly, the noise only occurs during the "space heat" cycle that operates the radiant floor heat. I've watched it go to 20% in the post-purge of the domestic hot water cycle several times without making any sound at all.
I won't tinker too much, and will keep my hands off the air/gas adjustment valves. But I've got to figure out this sound so my family can sleep again.

 

Your combustion analysis numbers are no where in line with Lochinvars recommendations.
If the tech says they are correct then he doesn't know exactly what he is doing. If it were me, I would have done a more in depth analysis and gas valve adjustments along with Lochinvars tech support on the phone. Seems to me that the burner itself may be damaged and or the air/fuel mixture must be properly set during high and low firing rates. His printout doesn't detail when, in the firing sequence, these readings were taken.

 

The modulation is usually only for a cost savings by using less gas on low fire. Is there any way to turn off the modulating feature to see what happens. At this stage of the game it's fuel savings vs piece of mind.

Since it only does it at low fire my guess would be the fuel / air mixture is not correct. I believe you are getting too much air at the lower percentages. If you want to play with this just mark the initial settings before adjusting and you might want to research techs that know what they're doing. As pp said I agree or at least I'm saying, That last guy had no clue, at least about the Lochinvar.

 

Thank you both! Judging by the combustion recommendations, my CO2 is high and my O2 is very low. I appreciate both of your help. I also got a callback from a Lochinvar tech this morning who verified that the numbers are off and gave me the numbers of a few other people in my area that could make the repair. The first guy I called said he'll make it right for $285 - much more reasonable.
I'm happy to let someone with the proper equipment and expertise make air/fuel adjustments.

 

ere,
Sounds like your on the right track. Hope this guy works out.

 

Happy to be of help

 

I would call the first guy back to finish his job. You now have the numbers for combustion, just have him set to spec.
Don't play with modulation numbers, doing so could cause short cycling increasing fuel cost and service problems.

 

Any update on this or have a corporate rep contact you could share that was helpful? Mine does the exact same, I've had three techs from 2 different companies check it out with no luck. Got the same recommendation for an expensive clean that did nothing, and a very expensive estimate to reroute a exhaust run which I did myself with no luck. If there was a way to keep the unit from trying to run at under ~25% it would not be a problem. Also hearing the local rep will only go through suppliers (according to the ones who don't seem to know what they are doing)

 

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