Noisy Munchkin

Alan (California Radiant) Forbes · February 24

This boiler has been flawless for 20 years and then slowly, it's starts making combustion harmonics. I've cleaned the HX, set combustion at 9% CO2 and then again at 10%, upgraded to the 926 board and replaced the burner in 2020 and last week, after no luck doing anything else, replaced the gas valve and swirl plate.

Separate intake air and exhaust. The owner sent me this video.

hot_rod · February 24

repairs to a 20 year old Munchkin sounds like risky business to me?

Was the burner cone in good condition? When they burn a hole through they can get weird. Is it the mesh type, or the slotted stainless tube?

kcopp · February 24

I would have guessed the swirl plate. There are several types… Are you sure that its the right version? How did the old one look?

Alan (California Radiant) Forbes · February 24

The burner looked fine the last time I cleaned it. Mesh type that I replaced 6 years ago.

And the original swirl plate that I removed looked almost new.

pedmec · February 24

What does your other combustion numbers look like with high fire and low fire? I'm assuming natural gas.

pedmec · February 24

What model munchkin do you have? i have one myself and installed plenty of those back in the day but i don't remember a rubber coupling on the top. it definitely looks different than anything i have seen with that line. i know that added a restrictor hose on the air inlet on some models when they were having trouble but not like i have seen there

GGross · February 24

The harmonics started before any of those parts were changed?

HomerJSmith · February 24

Certainly, an annoying vibration. It starts when the flame occurs. It doesn't happen when the blower is in pre-purge. I would look at supply gas pressure, gas connection to the boiler any partially closed gas valves, there should be two.

A mechanics stethoscope might pin point the origins of the vibration. I use one that I bought for my car. It gives a visual and audio indication from several locations at the same time. Not expensive. You should have one. An important tool.

https://www.amazon.com/ZKTOOL-Electronic-Stethoscope-Diagnostic-Headphones/dp/B09QLXV61Q?content-id=amzn1.sym.3be64970-3b95-4a6d-a45d-78077a3ff871%3Aamzn1.sym.3be64970-3b95-4a6d-a45d-78077a3ff871&dib=eyJ2IjoiMSJ9.Dt70O4WH6sRMlDEVrmJDwm2pzvWixPLQWREXip28MCVBPeazuteUj97WD5zTajuJms7MsD8dFfxqh9IMHLaypiRy0ObqnYg2ZwQpY4X8DITYAzFZDbZUCCGq6h-BZPM51w3eDshV-cYlzQHYOaJ20o0_CsjVDcrTBP-3ydwUzTuxVhP3bipQ1vViNUhlw9RseWhkl-FkrO5eqWgXFZSLRUGJeeLLNkLh57dNARG8lno.0T0Jzfbx9roLswJFdDLJR7FxKYWRrydYvmAF-LivUwU&dib_tag=se&keywords=automotive%2Bstethoscope%2Bkit&pd_rd_r=608901e6-374a-496e-ac63-9c97747277dd&pd_rd_w=GKWvW&pd_rd_wg=0Unnh&qid=1771940206&sr=8-20&th=1

Also possible that the gasket on the burner tube is incorrectly installed or leaky. Tighten the 4 screws on the burner tube really tight. just thinking what could vibrate. Is the gas valve pulling a vacuum?

Intplm. · February 24

@Alan (California Radiant) Forbes Has the gas pressure changed? What was it to start? What is the pressure now?

Alan (California Radiant) Forbes · February 24

Great pointers, everyone. I've done all the testing at various times and don't have the results documented. Maybe it's time to revisit and I'll get back to you.

The model is a T50M. That rubber Fernco coupling is common on some models.

From what the owner says, the sound started mild and then slowly increased in volume and duration over time.

Noisy Munchkin

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