" wrote:

The fuse is a 25A "Edison base" fuse in the switchbox on the furnace
itself.

There's no reference to the fuse anywhere in the manual.

I've lived here for 7 years, so the fuse is at least that old. The
house is 12 years old.

Sounds like the builder recycled an old fusible disconnect since they
haven't used edison base fuses for quite some time. New ones use
cartridge fuses, or they use small circuit breaker panels.

At any rate a problem might still exist since fuses usually blow as a
result of a problem, not old age. 25A is also a pretty large fuse and an
oddball size as well so it may not be the correct one, 20A or 30A would
be expected.

You haven't indicated what type of furnace this is yet (oil, gas, etc.)
but most would be expected to be on a 20A circuit since burners and
blowers don't take that much power. Possibly the blower bearing are
going or it's clogged up and is drawing more power than normal?

Possibly a pre-existing condition where someone overfused to 25A to mask
the problem? What size breaker is feeding the furnace from the main
panel? What gauge wire is feeding it if you can see? 12ga would be good
for 20A, 10ga for 30A.

Pete C.