Nest thermostat reading a fault “problem with a wire” diagnose and repair.
Oct 28, 2026
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Nest thermostat displaying a fault with a wire, and shutting down the system. Traced to a shorted contactor.
This
thing
said
it
had a
problem
with
the
W1,
with
the
W1
wire.
So we're
going
to do a few
tests here.
21
volts.
That's
a good
bit,
so I'm
going
to put
my amp
meter
on that.
I'm
looking
for a fuse.
It's
going
5
amps,
so
more
to
Gagin.
I'm going to cruise
across this real quick.
Going forward, I don't know if that will record it.
Jumping
from red
to white
again.
5 amps.
That'll
be
quick.
Back up
here,
contactor.
See if that doesn't clear up the problem.
To
even
get
back
into
the
thermostat,
The
heat
pump
came
on
and
started
running.
So that Nest thermostat kept a low voltage short
from burning up the contactor.
I didn't know they would do that.