Question about Honeywell Heating & Cooling

1 Answer

I've replaced my very old (mercury) Honeywell thermostat with a new one (round, Model: YCT87K1011), but I can't get it to control the temperature. If I connect the two wires one way, the furnace comes on but won't shut off. If I reverse the wires, the furnace doesn't come on at all. I've actually tried two of these replacement thermostats with the same results. Any suggestions? John

Posted by on

  • jharyyz Nov 06, 2008

    ***** -- thanks! But I'm not sure what you mean by "heat anticipator" -- the two switches on the back of the unit? I've set them as recommended for a gas boiler.



1 Answer

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that gotĀ 5 achievements.


    An expert whose answer gotĀ voted for 20 times.


    An expert who has written 20 answers of more than 400 characters.

  • Expert
  • 147 Answers

Hey John, man that ole T87 has been around for a hundred years and I have installed many of them, but I cant remember the letters on the wiring. Seems to me that it is R-W-Y, any way you will use the R and W. I have a t87 at home still in the box and I could wait till I got home to help you but Im sure its the R and W terminal. Dont forget to set the heat anticipator. Set it the same as the current value of your gas or oil valve.

Posted on Nov 06, 2008

  • butch welch Nov 06, 2008

    You did good. I am positive (100%) that you connect your wires on R and W terminals on the subase.



1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Round honeywell thermostat

Sounds like you have a T86 thermostat...take the round front cover off to view the Mercury switch. Watch the bulb when you change the temperature to a higher setpoint. If the bulb makes contact when rotating it up, and the furnace doesn't go into a call for heat, then it could be the thermostat, wiring, or furnace problem.

Dec 13, 2013 | Honeywell Heating & Cooling

1 Answer

Honeywell programmable thermostat - was installed per instructions in manual and now the furnace runs non-stop unless I move switch to "off." The old (round mercury switch) thermostat was wired red t

If you are unsure about which wire goes where, that may be the source of your problem. The color coding can be confusing when changing from old to new. I pulled the instructions for my Honeywell CT3400A thermostat and found you can call Honeywell Consumer Services at 1-800-468-1502 M-F 7:30 am to 5 pm CT

Mar 11, 2013 | Heating & Cooling

3 Answers

Replaced mercury thermostat w/Honeywell CT87K - doesn't work!

You need a specific thermostat for a Wall Furnace it is a Millivolt Thermostat and not a 24v standard thermostat....usually it will work anyway however if the powerpile (generator produces millivolts from the pilot light) is weak it may not be producing enough...or the Pilot light may be dirty and lazy...won't produce enough millivolts ...or you can have bad or dirty contacts or connections....or a combination of any of the above.....a 24v Thermostat and particularly a non-mercury thermostat has too much resistance in it for a millivolt your Wall Furnace (other than the fan) runs on less than 1 volt

Oct 31, 2009 | Honeywell CT87B ROUND HEATING&COOLING...

1 Answer

Wireing a honeywell thermostat

Bill ..You dont have a heat pump.This controller will not work for a conventional system. Get the right thermostat

Jul 24, 2009 | Heating & Cooling

1 Answer

Replacing Round Honewell Mercury Thermostat

try to get one that is made for oil heat, the installation is easy only two wires, and the instructions make it easy.

Oct 23, 2008 | Honeywell Electronic Programmable...

1 Answer

Honeywell round mercury thermostat - heat not coming on

If you tip the mercury switch so that it makes contact and the furnace doesn't start, it isn't the t-stat. Check the connections, then start checking the furnace.
In any case, ditch the mercury t-stat (recycle it properly) and get a new programmable one if at all posible. It will pay for itself many times over by turning your heat down in the middle of the night and back up by morning.

Feb 09, 2008 | Honeywell CT87B ROUND HEATING&COOLING...

1 Answer

Honeywell T86A3006 24V Class 2 Round thermostat 8020

The honeywell tradeline thermostat would work as a direct replacement (no mercury in the new ones), however if your using just heaters and no cooling system off of it, you could Heat only thermostat from honeywell that would replace your unit as well. Both at available at Ace Hardware with the heat only unity being roughly 7 dollars cheaper.

Jan 14, 2008 | Honeywell CT87B ROUND HEATING&COOLING...

Not finding what you are looking for?
Heating & Cooling Logo

Related Topics:

277 people viewed this question

Ask a Question

Usually answered in minutes!

Top Honeywell Heating & Cooling Experts

Bill Long

Level 3 Expert

588 Answers

Paul Carew

Level 3 Expert

3182 Answers

vance jones

Level 2 Expert

120 Answers

Are you a Honeywell Heating and Cooling Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides