wrote in message
...
All of a sudden my furnace blower runs constantly even though it is
set on "auto" at the thermostat. The heat cycles on and off properly
(fortunately because it is 19 degrees outside). The furnace is about
10 years old and is gas. I seem to recall there is a wiring option on
the motor for it to run constantly but no one has messed with that
since it was installed. I would appreciate any ideas on what the
problem might be.

Could be a sticking relay, could be a bad thermostat from the heat
exchanger. Try turning off all power to the heater and then turn it back on
and see if the blower stops when power is restored.