I recently bought a new digital Honeywell line-voltage thermostat to
replace my current one. The thermostat controls one 240V wall heater.
I'm having some trouble because the wiring is different on the new one
compared to the old one (and Honeywell doesn't provide directions).
This is my current thermostat and wiring:
Although the photo doesn't show it, the red wire from the thermostat
is wire-nutted to two black wires, the black wire from the thermostat
is connected to another single black wire.
Okay, so here is my new thermostat:
Can someone give me some advice on how to properly hook this up?
Looks like the new one is a LineVoltPro. You can find the specific
model here, then they have links to the installation instructions.
Likely your existing stat is only switching one phase, while the new
stat switches both phases.
You need to bring both conductors from the wall heater back to the stat
to wire it up the way they show.
Warning...the following makes sense electrically, but I'm not sure if it
is acceptable to code. I'd appreciate it if someone else could verify.
Unless the thermostat does something "intelligent" to monitor load, you
should be able to treat the new thermostat as a single pole switch, same
as your old one. This would switch only one side of your heater,
leaving the other hot all the time.
Take the single black wire connected to the black thermostat wire, and
hook it up to the inner black wire. Insulate the end of the outer black
wire--this will be live when the heat is on.
Split the two black wires hooked to the old red wire, connect the one
going to the heater with the outer red wire, and the one going to the
supply to the inner red wire.
On Wed, 29 Nov 2006 13:49:21 -0600, Chris Friesen
Hmm. I wired it up exactly as you described. Thermostat powers up
normally and runs through self test. I set the temperature, and I
heard it "click" and the display shows it's turning the heater on,
however, the heater never comes on. Any idea on what I could be doing
Hmm...I'm thinking I misunderstood the old one. I forgot it had only
two wires. I'm sorry, I gave you bad advice.
You should probably rewire the old one back in before continuing--the
two blacks hooked to the two red leads get nutted together with the old
red lead, and the other black gets nutted with the remaining black wire.
The two black wires that were nutted together with the red before should
stay nutted together. These are likely one leg of the supply (but we
can't be 100% certain without checking).
The black wire that was nutted to the black thermostat wire before is
likely one leg of the wall heater, but again, we can't be 100% certain
The white wires may supply the other leg of the circuit to the wall
heater, although ideally if they're hot they should be taped to identify
them as such.
If you have a voltmeter, check the voltage between the black wires (that
were nutted with the red before) and the white wires. If this is 240V
then you know that the black wires are one side of your supply, and the
white is the other.
If this is the case, then you can nut the black inner lead to the two
black wires, and the black outer lead to the remaining black wire. Then
nut the inner red to the three white wires and see if that works.
If you can identify that one of the three white wires goes to the
heater, then you could pull it out and nut it to the outer red lead,
leaving the inner red lead nutted to the remaining two white wires.
You have to first determine which of the three cables in the box is the
feed. Then determine which of the two remaining cables is the feed,
continuing to another heater, which should remain spliced to the feed. Then
the last cable is the one to the heater. Once you've determined this, you
can connect it like the diagram. Currently the thermostat is just breaking
one leg of the 240 volts. The second leg, the white wires are spliced
directly. The Honeywell stat needs 240 volts to operate, so you can't just
connect it to one leg like the current thermostat
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