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Upgrade Mears 602

I am upgrading our Mears 602 thermostat for baseboard heaters to Honeywell RLV4305A electric heat thermostat.  The instructions only state a 2 and 4 wire system, I have 6 which one set goes to the next heater. The new one has two black wires.  Attached are pics, sorry it attached them twice. 


  • bburd
    bburd Member Posts: 684
    You have a four wire system that requires a double pole thermostat (one pole for each hot wire on the 208-240 volt circuit).

    In your case the two wires to the next heater connect in parallel with the load of the first heater, so there are only two connections to the load side of the thermostat. The thermostat’s current rating must be higher than the total current draw of all the connected heaters combined. 

  • knl79
    knl79 Member Posts: 2
    The next heater had its own thermostat.  As seen in the pictures. The blacks on terminals connect to #3 black and white.  The red wires - one connects to both #1&#2 blacks and the second connects to #1&#2 whites.  Would I connect #3 black and white to the new thermostat black wires and leave the other #1 & #2 blacks connected together and wires connected together.    Please see pic of what one person suggested.  Also are some additional pics of cureent thermostat 
  • bburd
    bburd Member Posts: 684
    edited October 2022
    If the other heater has its own thermostat, then it should be connected to the wires on the line side of the existing thermostat you want to replace.

    There are four wires connected to your existing line voltage two pole thermostat. Replace that with a line voltage four wire thermostat of the same or higher current rating and make the connections in the same places. Simple.