This thread came at an opportune time as I just got three used round, mechanical, heat only Honeywell thermostats that I installed and have a few questions I hope someone here might answer.
The one Im having most trouble with is a T87F2873. It has provision for three wire hookup. Base plate states Red to R, White to Y and Blue to W. The system is hot water radiator and uses only two wires. Only way thermostat works is hooking wires to R and Y but it operates backwards. If I turn the set temp lower than the room temp it turns circulator on. If I turn the set temp higher than the room temp it turns circulator off. I knew it wouldn’t make a difference but I reversed the wires and it operated the same.
The other two I installed are not the exact same model as above (I don’t have the model number of them while I write this) and seem to be working okay but there are a couple things Ive noticed with them. Number one will allow the room temp to drop at least three degrees below the set temp and not call for heat. Just how much its allowing the room temp to drop before turning the circulator on Im not sure. How many degrees is acceptable? Should it be calling for heat when the room temp drops exactly to the set temp?
Number two consistently shows a room temp 6-8 degrees above the set temp. I realize that after being satisfied and turning the circulator off the room temp will continue to rise some but this is not the case. Im finding the higher room temps with the baseboard cold to the touch. So it seems the thermostat is keeping the room temp higher than what its set for.
What is the adjustment made with the copper colored pointer at the 5 o’clock position? The scale below the pointer has numbers 1.2, .8, .6, .5, .4, .3, .2, .15, .12, .10. At the right end of the scale is the word LONGER with an arrow pointing towards the left. For some reason the pointer on the T87F2873 will not move the full range of the scale like it does on the other two.
Thanks for any info anyone here might be able to give me.