Humming coming from inside boiler

Good Morning!

I am hearing a faint humming coming from inside my boiler and am trying to troubleshoot it. This is what I've discovered thus far.

1) If I turn power off to the boiler the humming stops.
2) If I turn the thermostat off but keep the power on the humming continues.

This very well may be a normal condition, but I had the boiler enclosed on three sides and may not have heard it before. I tore down one of the walls to access some piping before I fired it up. Yesterday we piped in a sprivent and bladder style expansion tank as well.

I'm not overly intimately familiar with everything concerning this boiler and am looking for things I should check.

Thanks in advance for any and all help.

 

Its probably an transformer or relay.

 

Many transformers make a hum at the line frequency rate (or double it) of 60Hz.

 

Sounds good! I look at the manual are there is an internal transformer.

Thanks again!