2

I have no AC in my condo, only hydronic baseboard heat, currently controlled by an old mercury thermostat. I have a new smart thermostat with a c-wire adapter I want to replace it. Trouble is, I’ve switched every darn switch on the panel (as far as having every breaker switch off at the same time), and the thermostat is still getting power/able to control the heaters. I live in a condo with a common boiler, and there are no zones within my unit, so all baseboards are either on or off, in case that’s relevant. Can I move forward and replace this thing without shutting it off first? This is a little outside my DIY realm of experience so any advice is appreciated!

4
  • 1
    Is this a low voltage thermostat? Most of the old Mercury were low voltage that I have come across. I would check with the building manager or maintenance person some smart thermostats are not compatible with some systems. I would expect your zone control to be 120v but it may be 24 or millivolt depending on the age of the system. You may not be able to simply add your thermostat so verification would be a good idea and they may have the only breaker for the community system. – Ed Beal Mar 25 '20 at 16:31
  • Thanks for responding! There is no building manager or maintenance, as each unit is privately owned. I’ll check in with my HOA, though. :) – Katidid Mar 25 '20 at 20:51
  • 1
    the condo has to have someone to contact about a community heating system if nothing else annual fire marshal inspections are required In my state. – Ed Beal Mar 25 '20 at 22:10
  • Yes, can you talk with your HOA/condo board? They have somebody who takes care of the heating system, or at least can point you at its documentation and such... – ThreePhaseEel Mar 26 '20 at 1:10
2

The reason you need to cut off power when replacing a thermostat is to prevent the wires from touching each other in the process of disconnecting and reconnecting all of them. Assuming it is using 24VAC control (you need to measure it to make sure it's not high voltage), you are not in danger of getting shocked, but if the wrong wires touch each other, it could blow a fuse or damage the equipment.

If you can't turn off the power (lets just assume you can't) then just be very careful and don't let the bare wires touch anything. The best way to do this is tape up each wire as it is disconnected and never have more than one wire un-taped at a time. Treat the wires like live voltage that could shock you to make sure you are being careful enough. A small touch of wires or touching the wrong screw could cause damage to the system.

If the thermostat has a separate mounting plate that the wires connect to, it makes it easier (most common these days). If the wires connect directly to the thermostat, you need to make sure the thermostat is completely off until all wires are disconnected and reconnected.

2
  • 1
    Tape the red, hot, until all the rest of the wires are connected to prevent accidentally touching it to something it shouldn't touch+ – JACK Mar 25 '20 at 16:34
  • 1
    I would say bad advice without more info on the system. the op could dump the entire system. it’s a community system we don’t know if and how it is controlled Some use 120v valves for control some use relays, we don’t have many boilers in my area but enough to say there are many different control methods and doing the wrong thing can take the whole system down. I know a few winters back 1 tenant took a friends heat system down several times we ended putting the pods on separate fuses and narrowed it down after the 4th or 5th outrage someone trying to put a smart thermostat in. – Ed Beal Mar 25 '20 at 22:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.