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C-wire - clarification

KMSNYC Member Posts: 31
Hello, I have a new Honeywell VisionPro 8000 to replace existing older Honeywell thermostat. Existing setup has 2 wires:
"R" (red) 24 volt AC from the transformer on the boiler (Burnham - steam)
"W" (white) sends the 24 volts back to the boiler relay to switch on the boiler.
Thermostat acts like an on-off switch.
VisionPro needs C wire to power the internet module (otherwise batteries would run down).
Can I simply run a new wire back to the other secondary transformer terminal (24 volts) to be the 'C" wire - and leave the existing wiring as is?


  • ratio
    ratio Member Posts: 3,675
    Yes, provided you end up connected to the correct transformer/terminal/etc., as Bad Things may happen if that's not right. Consider, however, replacing the wire with one of an appropriate number of conductors. It shouldn't be any harder than adding one (unless you were just planning on laying it along the baseboard!), and will be much more professional.