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anyone help with t-stat wiring?

i am replacing a white-rodgers 1e30-910. old model with mercury. it only has 2 usable terminals. there was a white wire hooked to the R5 and a black to a 4.

i purchased a honeywell 7400 to replace it and the instructions seem to indicate the 4 should go to the R on the honeywell but i am unsure about the R5. i would think that would go to RC, but i don't know. Any insight? honeywell isn't available until tomorrow........

Comments

  • Anthony Menafro
    Anthony Menafro Member Posts: 199
    Heating or cooling

    Is this just for heating or heating and cooling? If for heating, you only hook two wires and they normally go to R and W terminals.

    Anthony
  • tony hill
    tony hill Member Posts: 8
    heat only

    sorry--heat only, one pipe steam oil furnace.

    i just looked at the furnace and it appears the R and the G are connected???? only thing is the color of the wires are red and white, so they must change wires somewhere in the house.

    on edit: just traced it and white wire goes to G terminal on furnace (also honeywell control on my furnace) and black in my tstat turns to red wire which goes to R. so i assume i hook R to R and G to G????
  • Glenn Harrison_2
    Glenn Harrison_2 Member Posts: 845
    On a standard modern day thermostat...

    R is the power coming into the thermostat, and the W terminal is your heating terminal. The reason you have a G in the boileris the boiler manufacturer cheated a little by using a fan relay center, which would nomally be used on a forced air furnace with central A/C, to enegize ther boiler. By making R and G you are energizing the relay next to the transformer. In a forced air furnace G would go to G, and would be controlled by the fan switch on the T-stat. So in your case, R goes to R, and G in the boiler goes to W on the thermostat.
  • tony hill
    tony hill Member Posts: 8
    thanks!

    i have a pretty standard boiler--burnham model. wierd that they would "cut corners", they seemed to have a reliable reputation!

    but anyway, thanks for the knowledge!
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