Had a 98 probably same issue heater core plugged - reverse flush with
garden hose then forward flush then reverse again until flow it string
and clear water.  Real common issue did mine every fall before it got
cold.   Of course the tail ender and frame damage did that car in....

Cheer's

BTW search the web for taurus heater core plugged you'll get lot's of
hits

When was the last time the cooling system was flushed. It doesn't take much to stop
up the heater core. I once took a company van that had the same problem & criss-
crossed the heater hoses where they enter the firewall & the heat came back on & lasted
three months until I criss crossed them again.

All good replies. To carry the suggestions a bit further, first check
the temperature of the heater hoses where they go into the core. Both
should be HOT and the same temperature. (close to radiator hose hot).
If both are way cooler than the rad hoses, the thermostat  or heater
core plugging is suspect.

There was an issue with mid-late 90s Tauri with corrosion in the
cooing system. Your 2000 may or may not be effected.  It caused the
water pump impeller to erode and not circulate the coolant, among
other things.. Check the coolant in the radiator. If it is BROWN, then
you have this problem. There was a Campaign on this, but it may not
apply now. If the coolant is Green, then there is another concern.
 Your Taurus uses an electronic  Blend Door Actuator to move the heat
BLEND door in the MVAC system. BDA failures are common if the temp
won't adjust. If the hoses to the heater core are both good and hot,
(and the coolant is Green) suspect the BDA. (Usually requires
Instrument Panel removal to replace, yikes).