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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21386
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I am replacing a two wire Lux thermstat with a Honeywell

Customer Question

Customer: I am replacing a two wire Lux thermstat with a Honeywell RTH8500 I wired it as it shows red to RC and white to C The thermostat has power but when it calls for heat it doesnt get any from the boiler
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Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

Red to R white to W. The jumper between R & RC can stay or be removed it doesn't matter

Customer: replied 1 year ago.
That doesn't help me at all. That is how I said I wires it and it doesn't work.
Expert:  Rick replied 1 year ago.

You said " I wired it as it shows red to RC and white to C ". I said red to R & white to W. Not the same at all

Customer: replied 1 year ago.
The Honeywell RTH8500 says it will not work without a wire to C for powering the thermostat up
Expert:  Rick replied 1 year ago.

Then you need to run a separate 24 volt common lead to C but if you have a hot water or steam boiler you'll need 2 more leads to use the recommended work around. Besides the leads on R & W you'll need to install a new 24 volt transformer and run 2 leads from the 24 volt side of the new transformer to RC & C then remove the jumper between R & RC before you power up the new transformer.