This is the same older style Honeywell Triple
Aquastat relay with the cover removed
The Hi setting is the high water the boiler
is set at 180 degrees F is the average setting
The Lo is the low setting this is the setting
that turns the boiler on 20 degrees lower then
Hi is normal
The square thing on the right is a
transformer that takes the power from 120 volts
to 24 volts but beware the box has 120 volts
inside of it. just under the transformer is the
relay.