nest Thermostat E Guide D'installation page 9

5. Remove any jumper wires
Jumper wires are short wires between two
connectors. The Nest Thermostat doesn't
need jumpers. If your thermostat has jumpers,
remove them, but save them along with your
old thermostat.
IMPORTANT: If you have Rh and Rc wires, you have
a dual transformer system. The Nest Thermostat E
is not compatible with dual transformer systems,
but you may be able to use the 3rd generation Nest
Learning Thermostat.