How do I Wire a Honeywell Millivolt Thermostat?

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Things You'll Need

  • Screwdriver

  • Wire strippers

Many old boilers and furnaces use a self-generated millivolt system to heat homes.

Enjoy the added comfort and convenience that a new thermostat can provide by installing a Honeywell millivolt thermostat for your heating system. Millivolt systems, unlike conventional 24-volt heating systems, generate their own electricity. With a few tools you can easily wire a millivolt thermostat to your heating, ventilating and air-conditioning system.


Step 1

Turn off the electricity to your heating unit, such as a furnace or boiler.

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Step 2

Connect one thermostat wire to one screw terminal on your millivolt thermostat's wall plate. Millivolt heating systems use two thermostat wires for operation. Either wire can be connected to either screw terminal on your Honeywell millivolt thermostat.

Step 3

Connect the second thermostat wire to the second screw terminal on your thermostat. Make sure the insulation is intact around each wire. Bare spots in the wire can lead to future problems with your heating system.

Step 4

Turn the electricity back on to your heating system.


Check the insulation of both thermostat wires to ensure there are no cracks or tears. Exposed wire can short out the millivolt controls of your heating system. Old wire may have cloth insulation and a dark material directly on the wire itself. Scrape off the wire to ensure a good electrical connection.


Make sure the electrical is off to your heating system. Bare wires can touch and short out, damaging the control circuit for your furnace or boiler. If you are replacing an existing thermostat, the old thermostat may contain mercury. Consult your local municipality for proper disposal instructions.


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