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).
- 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
- 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
Me, I'd take the old thermostat out, carefully label the wires I
disconnected so I know exactly where they went on the old thermostat
(which may be helpful in transferring them to the new stat), and bring
the thermostat with me to a store that had some help that knew
If you want to kill some breakers, the ones that control the boiler
and fan are the ones to go after. Typically though stats run off low
voltage wiring and there's not much reason to worry.
Chris, last year I replaced the same kind of round mercury thermostat
with a battery powered digital one. I am a total home-repair newbie,
and it was a very simple job.
I just bought one that said on the box it worked with my type of
furnace (gas forced air) and followed the directions. It's a Honeywell
model and came with little stickers for labeling each wire as I
disconnected each from the old thermostat, so there was no problem
getting them matched to the right terminal in the new one. The
directions even had handy hints, like wrapping the wires around a
pencil so they wouldn't accidentally fall back into the wall. The
hardest part of the job was screwing in the teensy screws on the new
Don't bother with the round digital t-stats. If you're going to replace the
old analog t-stat, replace it with a -programmable- digital unit. They are
not round but the savings in heat (and cooling if you have a/c) will more
than pay for the unit in one year. They are more expensive ($50-150) but
much more worth it.
They're called programmable because you can program the unit to provide heat
when you are home and not provide heat when you are not home. Some are
"seven-day programmable" meaning all seven days can have a different
program, others are "5-1-1 day" meaning Monday-Friday is the same program
and Saturday and Sunday are separate, and then there's the "5-2 day",
basically one program for the week and another for the weekend.
The wiring is no different, so why bother with a non-programmable digital
Hey everyone. I've purchased a Honeywell digital programmable (5-1-1)
and I am totally lost with the wiring. My old mercury t-stat had only
two wires, a red and a white, with no labeling on the wires or the wall
plate. The new one has a bunch of lettered wire spots (W, C, RC, Y,
etc.) and they say in the manual not to choose based on wire color -
but I have nothing else to go on.
OK - the Honeywell page had a wizard that said basically to go by wire
color after all... so I did and it worked. First (albeit minor) home
repair project complete. Huzzah!
Thanks everyone for your help and suggestions.
You did not mention what kind of heating(and cooling?) system you have.
Installing programmable thermostat is good idea for energy saving.
Some needs batteries, some draws power from the furnace control power
source. Can't go wrong with any Honeywell brand. And they come with
installation, operation(programming) manual. When you work on them
turn the breaker off to the furnace. I installed Honeywell vision Pro
8000 commercial model in my house, downtown condo, and cabin.
This particular model can handle most any heating/cooling set up and
it is very easy to set up. Comes with 5 year warranty. You remove it
from base plate on the wall, program it sitting in your favorite chair,
when done plug it back onto baseplate. That's why it's called arm chair
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