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Old 01-26-2010, 12:31 PM   #1
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Replacing thermostat


Is it possible to replace a thermostat live? I've just bought a condo and I have no access to the boiler/furnace room and I want to install a digital programmable thermostat. I've installed them before but I always shut off the furnace. Can I just be careful not to touch any of the wires together?
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Old 01-26-2010, 12:33 PM   #2
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Yes. If you touch the wires together you will only complete the circuit and turn the burner on for the period of time they are touching.
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Old 02-19-2010, 10:13 AM   #3
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Is that the case even if they have more than 4 wires?
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Old 02-19-2010, 10:35 AM   #4
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Quote:
Originally Posted by n0c7 View Post
Is it possible to replace a thermostat live? I've just bought a condo and I have no access to the boiler/furnace room and I want to install a digital programmable thermostat. I've installed them before but I always shut off the furnace. Can I just be careful not to touch any of the wires together?
You bought a condo and have no access to the furnace? Why not? Do you have access to the circuit breaker panel to turn the power off to the furnace and AC unit? I would be reluctant to try to wire up the t-sat hot. Not that it is dangerous but you might cross the wrong wires and cause a problem.
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Old 02-19-2010, 10:55 AM   #5
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You bought a condo and have no access to the furnace? Why not? Do you have access to the circuit breaker panel to turn the power off to the furnace and AC unit? I would be reluctant to try to wire up the t-sat hot. Not that it is dangerous but you might cross the wrong wires and cause a problem.
No furnace in the suite, the building has a boiler with hot water baseboard heating. Each suite has their own standard thermostat. No A/C unit's. Asked the sales people and the building maintenance, no one knows or cares if it's allowed... "grey" area.
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Old 02-19-2010, 11:50 AM   #6
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Since in this case you are only taking a 2 wire t-sat that controls the circulator on the WH baseboard I think it is OK to work it live. Disconnect the 2 wires and install and connect to the like designated terminals on the new T-stat. You will need a T-stat with a battery powered option (most have it) as you will not have 3rd wire from the boiler to provide power.
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Old 02-20-2010, 05:50 PM   #7
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Is that the case even if they have more than 4 wires?
How many wires do you have?
Are any going to a "C" common terminal on the old thermostat?
If so, just don't touch the "R" and "C" wires together and you'll be fine
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Old 02-22-2010, 08:19 PM   #8
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Both wires are black. I know which one was where on the old thermostat, but does it really matter?
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Old 02-22-2010, 10:01 PM   #9
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Ok, I need some more advice. I attempted to replace it tonight and ran into an issue. Both wires are black coming out of the wall. One ran to "Y" and the other ran to "R" on the old manual Honeywell thermostat. These were the only two available terminals on this thermostat.

The new digital one has the following terminals:
H2
H1
B
O
RC
RH(jumpered with RC)
G
Y
W

The diagram for a two wire system says connect one wire to RH and the other to W. I did so and the heat comes on but will not shut off no matter what.

I tried RH and Y to keep consistent with the way it used to be wired, no change, heat still stayed on. I tried reversing the blacks on RH and W, no difference, heat still stayed on.

I tried removing the jumper, heat still stayed on.

I reverted back to the original thermostat, everything is back to normal. What else can I try at this point? Am I doing something wrong or is the thermostat defective?
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Old 02-23-2010, 06:13 AM   #10
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Why did you buy such a stat ? Go get a less complicated one for heat only.

I am not saying thats the problem but I think it's overkill.
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Old 02-23-2010, 10:23 AM   #11
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I can't seem to find anything that simple, everything is programmable digital these days. A simple digital manual 2 wire thermostat is all I need and if I can find one I'll go with that but in the meantime I'm still going to try to get the one I bought to work.
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Old 02-23-2010, 11:12 AM   #12
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Post the make and model of the new stat so we can look at the wiring diagram.
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Old 02-23-2010, 11:46 AM   #13
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It's a cheap RONA store brand model and the manuals aren't available online, I would have to scan the tiny book.

I went out and just bought the most basic digital Honeywell I could find, I'm going to try it tonight and post back with results.
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Old 02-26-2010, 09:20 AM   #14
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Alright, after much anguish and help from many others I've figured this one out. Turns out I have a reverse open valve system which means the heat is on when the circuit is open, similar to how air conditioning works. This system utilizes the R and Y terminals, not the R and W terminals. After three different thermostats, I've ended up with the Honeywell FocusPRO 6000 which understands and supports this type of system which had to be configured through the hidden menu. The cheaper ones won't do it.
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