Daniel Griscom
New Member
I had a Lochinvar Knight WHN 85 gas modcon boiler installed in the fall of 2014. It's worked well, except for one foible: when starting up from cold, it will often "hoot".
The hooting is at about 300Hz, and sounds like a foghorn or a French horn. It lasts for 2-20 seconds, easily audible indoors but even louder out of the supply and exhaust pipes (which happen to point at the neighbors' house). It only happens when the boiler is completely cold, and when a heating zone first calls for heat (not when the DHW tank needs heat).
A few months after the install, the installer came in with a specialist who was able to replicate the problem. He adjusted the air/fuel mixture and claimed to have fixed it, but the hooting still happens.
Here's a video of one such performance:
It starts with the cold boiler, and I call for heat. The unit purges, ignites, and then throttles down for efficiency. At about 35 seconds into the video it gets down to its lowest setting of 20%, and starts hooting. It hoots for about 15 seconds and then stops, probably because the boiler had warmed up.
I've done some more exploration of the problem. The supply/exhaust pipes are about 12' long, which is about three times the wavelength of the hoot, so it doesn't seem to be the pipes that are resonating (as a test I added a section of pipe to the intake while the system was hooting, and the pitch didn't change). I momentarily covered the supply pipe, and that immediately stopped the hooting. I'm guessing that it's the flame in the heat exchanger which is oscillating.
How can I solve this? The original plumber has retired two states away, and wasn't up to speed on the technical details anyway. If I hire another plumber, he'll probably see the problem once, twiddle the mix, not see it again (probably because the boiler had warmed up), and declare it done.
An update of the boiler's firmware could fix this, if the manufacturer wanted to. Is there any way to find out whether there are updates available?
Thanks,
Dan
The hooting is at about 300Hz, and sounds like a foghorn or a French horn. It lasts for 2-20 seconds, easily audible indoors but even louder out of the supply and exhaust pipes (which happen to point at the neighbors' house). It only happens when the boiler is completely cold, and when a heating zone first calls for heat (not when the DHW tank needs heat).
A few months after the install, the installer came in with a specialist who was able to replicate the problem. He adjusted the air/fuel mixture and claimed to have fixed it, but the hooting still happens.
Here's a video of one such performance:
I've done some more exploration of the problem. The supply/exhaust pipes are about 12' long, which is about three times the wavelength of the hoot, so it doesn't seem to be the pipes that are resonating (as a test I added a section of pipe to the intake while the system was hooting, and the pitch didn't change). I momentarily covered the supply pipe, and that immediately stopped the hooting. I'm guessing that it's the flame in the heat exchanger which is oscillating.
How can I solve this? The original plumber has retired two states away, and wasn't up to speed on the technical details anyway. If I hire another plumber, he'll probably see the problem once, twiddle the mix, not see it again (probably because the boiler had warmed up), and declare it done.
An update of the boiler's firmware could fix this, if the manufacturer wanted to. Is there any way to find out whether there are updates available?
Thanks,
Dan
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