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JBM HVAC, HVAC Technician
Category: HVAC
Satisfied Customers: 146
Experience:  Self Employed Air Conditioning, Heat Pump, and Gas Residential Installation/Service technician
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I just replaced my thermostat with a honeywell ct87k. I followed

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I just replaced my thermostat with a honeywell ct87k. I followed the instructions and I have three wires that were connected to the old thermo. red whit and green. I tried a few different combos and the heat (baseboard hot water) stays on past set temp. can anyone help?

Red is power

White is Heat

Green is fan


What terminals do you have hooked up to what wires?

Customer: replied 8 years ago.
i have red to red, white to white green dissconected, I have had the green in the only other place witch is dessignated yellow and that is when the heat wouldn't shut off.
Do you have the cycle set to #2 for a hot water boiler?
Customer: replied 8 years ago.
yes. switch 1 off, 2 on
Well you do have it wired correctly. This particular thermostat is just a single pole switch. The switch closes, power goes down the white wire, and the furnace goes on. The only thing that controls the cycles are the settings you put it on for determining which type of furnace it is. If the thermostat is allowing it to overheat more than 2-3 degrees past the set point then i would say that it is a defective thermostat
Customer: replied 8 years ago.

so if i touch all three wires together, the heat should come on right? Also since there is no mercury switch how level does it have to be?


If it is not 100% level it should be ok as long as it is close. It shouldn't have too much of a bearing if there is no mercury. Well if you touch the red and white wires together the heat will come on, Green is usually for a fan, i'm not really sure what it is in your application since you don't have a fan. So really green should do nothing, unless you have air conditioning as well, then green would be fan and yellow would be cooling

Customer: replied 8 years ago.

is there a way to test the thermostat with a continuity tester?

when i touch the red and white the boiler doesn't turn on. but now i touched the green and red and the heat came on so i guess the wires were wrongly coded, on the old thermo the colors were green red white in that order from top to bottom

What terminals were they attatched to?
Customer: replied 8 years ago.

how could i tell? iam not understanding the question


Sorry, i meant on the old thermostat. You said it was wired green red white top to bottom, what terminals were at the top middle and bottom?

Customer: replied 8 years ago.

like this:






I dug the old thermo out of the trash and the front of it (the actuall thermostat) was paired up to the back plate (the wires from the boiler) like this ? to green red out of wall to white on thermo & white out of wall to yellow on thermo. i guess i should repeat this setup on new thermostat?

your best bet would be to wire it up the same way. They definately did not wire that "correctly" Technically its wired correctly because it worked, but they did not use the standard procedure.

They have:

Wire = purpose (suppoced to be)

Green = Power (Red)

Red = Heating (white)

White= Cooling (yellow)

Customer: replied 8 years ago.

yea i hooked it up the old way and it is working, they had it labled wrong to.

they had it labled blue black and red when the wires were red white and green. its the last time I hire a colored blind one eyed chinaman to do hvac work.

Haha yea, not so good of an idea


If you need anything else please feel free to ask!

JBM HVAC and 3 other HVAC Specialists are ready to help you
Customer: replied 8 years ago.

thanks for your time, soon i am going to need to know how to dissconesct the base board hot water in some parts to hang dry wall and install shut off valves. talk to you soon


Ok, i'll be around. Have a good night!
Customer: replied 8 years ago.
thanks for your time. soon i will need to know how to dissconect the baseboard hot water so i can hang drywall. Jeffrey
Your welcome, sounds good!