Baxi Luna combi boiler - HT330 is it 'kettling' or something else?

jetpeach_2

Hi folks, I would really love any help if you all can identify what's happening in my boiler.
This video shows it all, with sound to help debug:
https://www.youtube.com/watch?edit=vd&v=fY7rAYZu05g

The boiler is on natural gas, I recently cleaned out the chamber, replaced the rear refractory insulation panel which was starting to crumble a bit, and calibrated it to about 8.4% CO2 on both the high and low fire settings.

It is not apparently fine on high fire, when hot water demand is on. But when heat is called for on low fire it does this rumbling/vibrating.

Is this what they call "kettling"? Or perhaps I am still mis-calibrated? I am concerned by combustion analyzer itself might need calibration, and if it's wrong then I am actually calibrating it incorrectly if the gauge is wrong... but the flame looks nice and blue, and in the past as I adjust the gas set pressure screws, if things are too rich or lean the flame color usually doesn't look so nice. So while reading forums and researching, I'm still at a loss to identify the issue.

So any help would be greatly appreciated!
Thanks,
Joe

Tom_133

it doesn't seem to be kettling sounds a little like mild fog horning due to bad combustion settings. Its one of the reasons I stopped putting in Baxi's they are very finicky on settings and hard to keep on high fire long enough to get it right. You seem to indicate its a low fire problem, so it may be easier to fix, just make sure its a calibrated analyzer.

jetpeach_2

Thanks Tom, I've definitely experienced the issues when calibrating on high fire - once the water in the hydronic system gets hot, it shuts off and I can't keep calibrating! So I usually end up calibrating high fire not using the calibration mode that goes through the hydronic pipes but instead in DHW-demand mode, by running the bathtub full hot, although I haven't known exactly what true % modulation is in the mode (although it should represent the maximum the house would ever call for).

I'll see if I can find a way to test the accuracy of my combustion analyzer.

If anyone has any more thoughts, I'd still love any other guesses, since I may want to order some extra parts as a just in case.
Cheers,
Joe

superdave

Just seen this sorry how did you make out. Is this Baxi on NG or LP?? How many zones are on system If you heat loss is small what I do is fill the boiler from the blue valve under Baxi and flush through the supply side so all return water is cold. What is gas PSI at stand by and what is it running on high fire how long is venting. High fire should be about 8.7% CO2 depending on gas PSI and low fire 8.4% CO2. Has any one changed the fan speeds on QAA73. Also when I get a call out on boiler we don't install if we have problems getting the CO2 just right I check the screws to see if other turned them way out of spec.

jetpeach_2

Hi there - thanks for the response superdave.

So I finally decided to hire somebody, and found NW Mechanical (a company in Seattle) had some experience with these (it was hard to find a company in the NW that was actually familiar with these), and after he cleaned and re-calibrated, the problem went away. I believe my combustion analyzer, which I hadn't re-calibrated in a couple years, has fallen out of spec, so when I last re-calibrated the flow on the boiler, I was actually setting it to the wrong gas settings (it is on NG) - I still have yet to check my combustion analyzer to confirm this but pretty sure this was the problem.
He did say that if the calibration is not quite perfect on these, they have a tendency to do this. And most importantly, the problem went away after he worked on it :-)

superdave

great glad it worked out for you.