Newb Question - Changing Thermostat, Power related

Old 10-31-13, 01:24 PM
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Newb Question - Changing Thermostat, Power related

So i'm a newb to homeownership, but i have relatively decent common sense, and know my way around the Do's and Dont's of DIY.

Our home has Oil heat hot water radiators, 2 zones (main floor, and second floor) and 200 amp electrical with the main fuse panel down by the burner (burner is only 4 months old. Previous owners put in a brand new one prior to us purchasing the home). The thermostat on the first floor however is ancient. So i'm tasking myself with replacing it with a new Honeywell touch programmable. Wiring it up is simple enough and easily within my realm of experience, however i want to verify something before i tackle it......

Power wise, everything i've read says cut the power to the thermostat before working on it to prevent shock (obviously self explanatory) however is the thermostat ALWAYS tied into the power for the Oil Burner? Or is it possible its on another separate power line.

I ask just because i cut the power to the burner last night, but the old school analog thermostat still "clicks" when i turn the dial to the on position from Off where its been all summer. Now i'm not sure if this is just a mechanical sound, or if its indeed electrical and the Stat is pulling its power from somewhere else that wasnt turned off when i shut down the breakers for the burner. Obviously quick and easy fix would be to turn off the mains to the home, but i feel like thats extreme and silly for such a quick job.

So the power pulled from the Burner, and the clicking i'm hearing is just mechanical? Safe to shut off the breaker for the Burner, and go to work?

**Plus keep in mind, this has been an adventure into finding out what breakers control what because the previous owners didnt do ANYTHING when it comes to reasonable maintenance, so the panel is really confusingly labeled, if labeled properly at all, and has already put me in potentially dangerous situations a few times when working on the pool filter system haha**
Old 10-31-13, 09:15 PM
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All you need to do is shut the power to the boiler before changing the stat.

There should be a disconnect switch right beside the boiler - usually just a run of the mill light switch.
Old 10-31-13, 10:37 PM
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Last question first; As soon as possible you should set aside a couple of hours to "map out" your electrical system. This means that you want to determine EXACTLY which circuit breaker controls each and every electrical switch, receptacle, fixed appliance, exhaust fan, light fixture and every single thing electrical in the entire house, garage and any outbuildings. There are several ways to do this and all it takes is a test light and time. You WILL be running back and forth a lot so if you can enlist a helper it makes it a bit easier.

Make a sketch of every room and mark the location of every switch, receptacle and light or other device. Turn the individual circuit breakers off and on individually until you KNOW which CB controls what. Mark that down on the sketch next to the device. Circuit breakers are numbered in the panel with the odd numbered CBs on the left and the even numbered CBs on the right and from top to bottom. Do not include the main CB in this numbering plan. Once you have the sketches you can then make a Word doc detailing the "panel schedule" or you can do it in an Excel spreadsheet format. The Word doc allows for more detail in what is controlled by which CB. Some people advocate using a permanent marker and writing the CB number on the back side of the plate covering the switch or receptacle but I prefer to use a P-touch label maker and using the clear tape actually print the circuit number and apply it to the face of the plate.

Now on to the main question. 99% of all thermostats WILL be powered after the safety switch of the heating system. There is such a small number of systems that might have been miswired to allow power ahead of the switch as to not be too concerned. These miswired systems would almost exclusively be area zoned systems and most likely NOT installed by anyone who really knew what they were doing or possibly in an older house. The vast majority of fuel-fired heating systems use a low-voltage for the thermostat, 24 volts AC is almost universal but electric heating, especially baseboards and in-wall unit heaters may use line-voltage thermostats that typically run at 240 volts AC. You can tell a low-voltage thermostat by the use of small diameter (gauge) wires whereas a line voltage thermostat will have larger wires.

The low-voltage thermostats are NOT a shock hazard but the systems DO often have a fuse in them and unintentionally touching one wire to another may blow that fuse. Turning off the power eliminates that possibility unless you make a grievous wiring mistake. Follow the instructions included with the new thermostat EXACTLY and you will have no problems.

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