Here is my situation:
Guardian 80% GG8S120C16MP11A; 2 years old
A few months ago, I installed a new thermostat (Honeywell RTH2300B1012/A), and
replaced the two wire with a three wire. Everything ran fine, no issues.
Yesterday, we had the gas line added to the existing water heater gas line. The
furnace has its own gas line running from the main line, and nothing was touched
running to the furnace. We shut down the main gas and turned the thermostat to
"Off." My spouse may have turned it back to "Heat" and turned the temperature
way down when the furnace didn't turn off right away, but in any event the
furnace did not turn on at any point during the gas line work.
After the work was complete, we powered up the water heater and then the
furnace. Both ran fine, however, the furnace kept running, and running, and
running (blower and heat). When it was 75 degrees, I realized we had a problem.
Here the steps I proceeded to take:
- Turned the thermostat down, waaaay down, and the blower and heat (gas) kept
- Turned the thermostat to "Off" and it (blower and gas) kept running.
- Powered down the furnace and disconnected the thermostat wire at the
thermostat. Powered the furnace back on and the blower and heat kicked right
- Checked the LED fault code on the furnace control panel: Long red flash, which
is identified as flame was sensed when there was not a call for heat. This makes
sense to me, as that is exactly what is happening.
- Powered down the furnace and disconnected the thermostat wires in the control
panel in the furnace. FINALLY I heard the furnace power on when we turned it
back on, but this time the blower and heat DID NOT turn on.
So it seems to me that the issue is with the wiring, not the furnace and not the
thermostat, as it still runs the heat and blower when the wiring is fully
disconnected from the thermostat. Can someone help me identify what is going on?
Is there a short in the wiring? There is a portion that I had to cut and
re-splice--could this be the issue? How would I troubleshoot this? Thank you!
Did you turn off power to furnace to stop it from running?
When power is back on start running again? If you suspect short
in wiring, disconnect wires from thermostat at furnace end
to see what happens. When you say you hooked up 3 wires with
new 'stat they are W(heat), G(blower), and R(control power 24V AC)
On Sunday, January 18, 2015 at 5:44:05 PM UTC-5, Marta Jensen wrote:
Not that it probably matters, but what was the purpose of this new
The furnace has its own gas line running from the main line, and
Maybe, but the part about the trouble code saying that flame was detected
when there was no call for heat doesn't fit in. If the problem is with
the wiring between the thermostat and the furnace, ie a short, then the
furnace would think there *was* a call for heat.
But I'd focus on the obvious. Disconnecting the thermostat doesn't stop the
furnace from running. Disconnecting the thermostat wiring from the furnace
does stop it. That points, as you say, to the wiring. So, I'd probe out
those wires, check out where the splice was
made. Any chance the gas pipe work damaged the thermostat wiring? With
a VOM you could test for a short among the wires.
How many wires. Do you have AC? AFAIK it's usually two wires for heat
and two wires for AC. They're color coded. Make a drawing of all the
wires, their colors and which screws they go to (even in a case where
they may be on the wrong screws, you still need to know what screws they
You know this because little lights went on, on the furnace??? What did
you hear? (I don't have a gas furnace>)
I was going to suggest a short right at the furnace control board,
before it got to the wires, maybe something just lying on the screws,
but what you say above seems to exclude that.
However, before you spend much money, you should reconnect, perhaps one
at a time, all the wires you've disconnected, starting the furnace after
each reconnection, to verify that it really is a shorted wire.
I've been thorugh this twice, where I assumed my last step had shown
where the problem was, but it was misleading***.
There must be.
Could be. Why would you have to cut or resplice a wire?
A volt-ohmmeter is often helpful but might not be needed here.
I wrote the line above earlier, but now I think it's your next step.
I'd get a voltohmeter, also called a multimeter, for about 10 or 20
dollars**. They also measure resistance. With the wires disconnected
at both ends, from both the furnace and the themostat, I'd measure the
resistance between each pair of two wires (of the wires that go from the
thermostat to the furnace). All the thermostat does is connect two of
the wires when it wants heat, and if they're connected already, you'll
have heat all the time. Maybe someone nailed something into the wall
and shorted two of the wires together.
If two of them ARE shorted, but there's another color that's not used,
you can change one of the shorted wires for the unused one. You should
attach a note to the furnace and one inside or behind the thermostat
explaining what you've done. For the next tech and you too, since
you'll forget what you did in a few years.
Temporarily you could use one of the AC wires, if they ae there, for the
Otherwise you'll have to find the short by looking for recent nails or
staples etc. or run a whole new wire. You can run the wire outside of
the walls. for a while. You can move the thermostat to a place where
the wires are shorter, but in most houses, the thermostat has been
positioned away from drafts, away from the sun, etc.
For the money it would take for a pro to run a new wire, you'd be partly
on your way to buying a portable wireless thermostat
**Don't get the smallest cheapest one, but the one that's one step more
expensive. At radio shack they also have a bag of 10 colored wires,
5 pairs of two, with alligator clips on each end. About $6 iirc.
Well worth it so you can clip one meter proble to one wire or one place
and you only have to worry about the other probe. There are loads of
uses for the meter and for the wires. (My car once stopped in its
tracks and I used a jumper wire in the engne compartment to get it
running again. Ended up driving that way for 2 years, but I remembered
to take the wire when I jumked the car. )
***One summer right after high school, my cousin gave me a car and the
battery was always dead. For a meter, I only had a 110volt light bulb
and an ice pick. No quick connectors on a '50 olds so I unscrewed one
connector after another until the test light stopped showing a short.
That meant the last thing I disconnected was where the short was, but
when reconnecting to test that, the short was still gone. Long story
short, it was the glove box light. Every time I opened the box, if the
light had been off, when I shut the door, I left it on, and vice versa.
And it was the light that was running down the battery. No direct
application to your situation, but you should still verify that the last
wire you disconnected which stopped the furnace, that it starts the
funnace when you reconnnect it.
replying to micky , Marta Jensen wrote:
THANK YOU so much to everyone for your quick and thorough responses. I think a
number of you were on the right path. I do not have AC, so that wire would not
be interfering with the connections. I did one final troubleshoot where I
disconnected ONLY the red wire, leaving the white and green intact. This
resulted in power to the furnace, but the heat and blower stayed off. This made
me think that there was an issue with the red wire. I ended up deciding to spend
all of 9 dollars and an hour of my time to replace the thermostat wire, as it
seemed the most reasonable and cheapest route to go. Thankfully, the suspicions
of a shorted wire were CORRECT!
I'll never know if it was sheer coincidence that this happened on the same day
that the gas line was worked on (inches away from the thermostat wire), or
whether something happened to the wire to cause it to short out. The wire had
been spliced as I did not have enough length originally, so that probably had
something to do with it.
Thank you again to everyone for the thorough and thoughtful feedback, I really
appreciate your help!
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