Hello group. I had a typical round mercury wall thermostat until a
drunk guy (no, not me :-) shoulder-planted into it and busted off the
dial. I'm thinking of replacing it with a battery-powered digital model
and a preliminary Internet search indicated it should be a pretty
simple two-wire job. But after reading some posts in here I'm a little
more concerned (I'm a fairly new homeowner and not super handy).
Questions a

- Do I need to cut the power to the gas boiler, the hallway, or both?
- I'm totally lost with voltage compatability issues - how do I
determine this?
- If I totally screw this up, how will I know (other than the
thermostat not working at all)?

Any help and advice will be greatly appreciated. Thanks in advance.

- Chris, home repair newbie