I suspect that I have two swapped wires in one of my thermostats that control the house heat. (The ones marked R and C). Does anyone out there have any knowledge as to the ramifications/symptoms/behaviour of such a mis-wiring?
If it is a two wire thermostat you would be fine.
I need a little info on your thermostat - is it a standard thermstat or an electronic one? Does it have multiple stages of heating and cooling? Do you know the brand of thermostat? etc.
Generally speaking, the terminals in a standard thermostat are
R (red) - 24 volt power
Y (yellow) - Cooling (B (blue) for second stage cooling)
W (white) - Heat (W1 and W2 for two-stage heat)
G (green) - Fan
Another common option is to have RH and RC instead of simply R. This is for when the heating and cooling have separate 24 volt power supplies. In most cases they don’t, and these two terminals are wired together.
A heat pump thermostat will have all of the above plus O (orange) - changeover valve and a few other colors as well. Will often have C (black) for indicator lights.
AFAIK, a C by itself would indicate Common (the neutral side of the 24 volt transformer) and is used to provide power for the thermostat itself - for a clock, indicator light, etc. I can think of two possibilities if the R and C were swapped - either everything would work, or nothing would. Check the other end of the wires, at the controlled device, to determine if it’s a problem or not. This requires some basic understanding of electricity and troubleshooting skills. Don’t rule out calling a professional.
And as boytyperanma pointed out, if it’s a 2-wire stat for something like electric baseboard heat or hydronic valve control, it won’t matter if they’re swapped.
It’s a three zone heating system. The thermostat in question controls one of the zones.
It is an old Honeywell rotary/mercury style thermostat. I feel it doesn’t do the job properly as seems to overshoot the desired temperature. I want to replace it with an electronic (programmable) thermostat. I bought one at HomeDepot and
while investigating the wiring on the old unit I noticed the wiring colors didn’t match (R wasn’t red). I know that’s not mandatory, but they match on the other two thermostats. I am concerned that if its wired backwards that I might fry my new unit (which wasn’t cheap).
Thanks.
Ooops big mistake. It is the R and W wires I’m talking about. (not R and C) Again, I am suspicious that these are swapped. Can anyone describe symptoms I would see if this were the case?
Could a mod rename this thread to Switched R-W wires on thermostat?
Thanks.
What is it about those old round thermostats and installers not using the color codes? Had the same problem myself a few years ago.
What you’ll need to do is look at the other end of the wires at the furnace, and see if the wires are on the expected terminals or not.
Ah, that’s the gotcha. There are three zones and all 6 wires appear in a big nasty bundle at the other end and I cannot differentiate the three sets.
So each stat has only two wires? If that’s the case, there’s no problem as thermostats run on (IIRC) 24 volts AC, so there is no polarity.
It’s when you get into things like cooling, blowers, heat pump, emergency heat and the like that the wiring gets tricky, but it sounds like you just have three utterly plain and basic hot-or-nots.
As already posted by many, if there are only two wires, then the only thing it can be doing is opening and closing a switch. In this case it makes no difference which wire is on which terminal. When it gets cold, The R and W terminals are connected. When it gets warm enough, the switch opens. Polarity is not a concern. As long as your fancy new thermostat is battery powered (most are), then there should be no possibility of frying it.
The main issue is not the wiring, but the performance of the thermostat. There are several reasons that a thermostat might overshoot, but the most common are
a.) Poor placement - the thermostat is in a bad location for sensing the room temperature or on an outside wall that is appreciably cooler than the rest of the room, etc.
And b.) an improperly adjusted or failed heat anticipator. In a standard thermostat this is a tiny little heating coil that pre-warms the thermostat a little bit because the air in the room will be uncomfortably warm before the thermostat senses it. The thermostat is attached to the wall and walls heat up much slower than air. The heat anticipator is adjustable. If the unit is overheating the space adjust the anticipator for shorter cycles (there is a marking on the anticipator that tells you which way to make the adjustment). If the anticipator has failed, the cycle times will be much longer, leading to severe vershoot.
Digital thermostats use a different method for achieving heat anticipation which IME is not adjustable. So your replacement thermostat will eliminate the second possibility and hopefully your problem will disappear.