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Thermostat Honeywell T87

philgphilg Posts: 4Member
I have a gas burner steam heat.

I recently replaced my mercury thermostat with a non programmable Honeywell T87.

The first problem was with the wiring. The old setup had a white wire and a green wire,

the red wire was pushed into the wall. I pulled the red wire out and connected W to W

and R to R but the thermostat would not work unless it was W to W and G to R.

The thermostat works but the heat is very uneven and the radiators are very hot or very cold between cycles. It seems like the room temp has to drop quite a bit before the

thermostat turns on the burner.

I have tried 2 different thermostats and they both work the same way. The old mercury

had an adjustment to anticipate when the unit would turn on/off.

Is this a wiring problem or is the way the new thermostat works?


Phil Gribbins


  • J.R. MaddenJ.R. Madden Posts: 10Member
    T-Stat Problem

    First lets tackle the wiring. Most of us use the R & W terminals with the appropriately colored wire. Someone for some reason substituted green for red in your case. This could be because the red wire was too short or damaged inside the casing. Disconnect wiring from all controls. Connect the red & white wires together in the basement. Take a continuity tester and check for continuity at the thermostat location. If you have continuity you can then connect the red and white wires to the appropriate terminals at both locations and all should be well.

    Second check the location of the thermostat. Is it mounted where it may sense temperature from a heat source before the who;e system warms up. I once ran into a situation where the thermostat was only 5" away from a concealed steam riser in the wall. As soon as the riser warmed up it satisfied the thermostat and shut the system down before all units were hot. A lamp placed too close to the t-stat can do the same thing! The new digital T-87's can be set to sense a 1° temperature differential. That is a 1° rise in temperature will open the contacts and remove the call for heat. Set the internal switch for a 2° differential and this should help.

    Third check the main vents on your system as well as the radiator air vents. If heating is uneven the thermostat has little bearing on that situation. It only senses temperature changes at the location where it is mounted. It doesn't know what is going on anywhere else in the building.
  • Jean-David BeyerJean-David Beyer Posts: 2,629Member

    I did not know that some thermostats had adjustable differentials. Mine do not, at least according to my manuals.

    A wise friend that this to say about thermostats (and not just home heating and cooling thermostats):

    A thermostat acts to keep itself comfortable.

    That was to remind people to locate them(thermally) close to the thing whose temperature was to be controlled.
  • Matthew GrallertMatthew Grallert Posts: 109Member

    On the back of the Thermostat two dip switches.  Both should be on.  Are they?

    Everyone Else's comments are right on.

This discussion has been closed.


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