Tankless water heater humming????

[andis65]

I installed a Bosch aquastar 240fx for my radiant heat flooring. It's running as designed, temp is fine, but it hums quite loud right underneath where the flue exits the boiler. Its not constant, it will hum then operate quietly then hum again. It's related to water flow, my system has a 3 speed circulator pump and I can get it to change sound by changing speed. The fan runs quietly after the unit turns the flame off, so it's not that. Almost sounds like expansion but it doesn't reach a happy spot. Anyone have any ideas???

 

[anthony666]

vague ideas;

-first thing i'd check is if you got the inlet/outlet backwards .. they usually make fish tank bubbling angry sounds when backwards, but it's worth a look

-did you ream the copper pipe after cutting it ?? i've seen (heard) some weird whistling sounds made from burrs inside the pipe .. like the sound of running water backwards through a valve

-another thing i'd look for is wind blowing down the venting .. ive heard stuff that sounded like a dog whistle to fog horn booming from venting

you want more specific help give us some piccys

 

[andis65]

turns out after trying several things, simply lifting up on the fill vale lever and introducing city water pressure to a 12 pound system for only one second pushed the air through the heat exchanger and solved the problem!! maybe since the heat exchanger is above (like 12") the outlet port on my tank less water heater the 12 pounds of water pressure couldnt force it out?? who knows... working great now though!! thanks for all the help building this system!!

 

[anthony666]

looks good man, nice and clean

 

[NukeMech]

About time....! I have work to do in YOUR shop...lol.