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Hi,

I recently bought a Honeywell thermostat RTH7600D to replace a old thermostat (containg a Mercury tube) in my condo.

Heat pump is 20+ years old Climatrol 753-2-18W-10.

The old thermostat is a Kepro 1262-1 (?) and had the following wires connected form the heat pump.

Green wire to G-F
Yellow wire to Y-C
Red wire to R-V
Black wire to W-H

I've followed the Honeywell instructions and connected the wires as follows:

Green to G
Yellow to Y
Red to R
Black to O/B (? )

Cooling works fine but when I turn the heating on and set the temperature to higher than room temperature it keeps on cooling - which seems to indicate that the changeover valve is not connected properly (tired both setting it to 0 and 1 in the thermostat options).

Any suggestions?

Thanks.
Thomas