You are fortunate that the unit continued to function. There are
several brands that go to continuous fan run to tell you that
something needs attention. Most recent units have an electronic
control board. There should be a standard "flash" chart on the
inside of the blower cover that has the wiring diagram. Count the
number of flashes on the board - the chart would tell you what to
trouble shoot. There is a daisy chain of safety relays usually
with the same color wire looping them together. There is a small
reset button on each of these. There is also a limit switch on
the burner box and a switch if the power venter doesn't come on.

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______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




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.