Honeywell RTH2510 Quick Installation Manual page 8

Quick Installation Guide
Connect Wires (cont'd)
Conventional Systems (Alternate Wiring)
Do not use C, C1 or X wire. Do not use B wire if you already
have O wire. Wrap bare end of wire with electrical tape.
This thermostat cannot be used if your old thermostat had
any two of the following wires: R, RC, RH, 4 and V.
Place a jumper (piece of wire) between Y and W/AUX if you
are using a heat pump without auxiliary/backup heat.
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6.