Page 202 of the manual clearly states that the instrument has a built-in power source that heats the cabinet to some degree and is not an indication of trouble.

I personally don't think there is a good comparison between "Block" and "Close" for a Shearing sound. "Block" is by far the better choice. "Close" is based on three notes of harmony whereas, "Block" is based on five notes, which is more what Shearing used. It also is a much more advanced and pleasing sounding harmony regardless of use.