Black is hot, white is neutral, and green is
ground. You test at the little box I mentioned
If it's the 31 code, I suspect you've got a bad
limit switch, not enough air flow, and the limit
switch finally gave out. I've seen two of those,
this year so far.
Christopher A. Young
Learn about Jesus
trader_4 wrote, on Mon, 22 Dec 2014 06:51:01 -0800:
I'll check that the white (neutral) has no voltage difference
with green or bare (ground), and that the black (hot) has
line voltage (120VAC) to both the neutral and ground, but, like
you, I am 99.9% sure that can't possibly be the problem.
The problem is "probably" described in this flow chart though...
With that clogged air filter, I'd be thinking
bad thermal limit switch. I replaced one this
year in my own furnace, and one about a week
later for a customer.
Christopher A. Young
Learn about Jesus
trader_4 wrote, on Mon, 22 Dec 2014 08:21:13 -0800:
OK. Fair enough. I haven't looked hard enough mainly because
I really don't think the problem is a reversed polarity on the
First off, the thing is AC, so, "most" AC items don't care
whether the hot or neutral are reversed anyway; but more
importantly, nothing was done to reverse the hot and neutral.
Looking at my pictures, clearly the line voltage comes in right
at the middle, from the overhanging flexible metal BX cable:
So, I'll pop off the cover of the box on the inside of that
connection - but - really - that will just tell me what I already
know must be the case - which is that the AC "line voltage" isn't
But, I'll check it - and report back - with pictures.
trader_4 wrote, on Mon, 22 Dec 2014 08:21:13 -0800:
I agree that hot and neutral *can* be reversed, but, from a practical
standpoint, other than the safety of two-wire grounded items, it
makes no difference.
So, when they're talking polarity reversal in the continuous-blink
scenario, I wonder if they're talking about the DC voltage, where
polarity can make a huge difference.
I doubt either one was reversed, simply because nothing was touched,
but, methinks they may be talking DC and not AC anyway.
Nonetheless, I'll pop that box off in the middle of the furnace
and measure the voltages (yes, I know what all the colors mean,
including white, black, red, if it's there, and green or bare).
I didn't check if it's 220V, but that just means there will be
two hots and a neutral, instead of a hot and a neutral.
Stormin Mormon wrote, on Mon, 22 Dec 2014 12:49:48 -0500:
I gathered the testing equipment:
I turned off the wall switch (it's turned on in this pic):
I removed the cover of the inlex box from the BX cable:
I separated the hot (black), neutral (white) & ground (green):
Turning power on, I tested neutral to ground at 0 volts AC:
Turning power on, I tested hot to ground at nominally 120VAC.
Turning power on, I tested hot to neutral at nominally 120VAC.
I turned the power off, and reconnected the wires as before.
If the power is reversed, it's not at the inlet BX cable
connection to the unit.
What I mostly want to find is the big red button that says
"reset", but I don't see it. I see a bunch of smaller limit
resets, all of which I've pressed already.
trader_4 wrote, on Mon, 22 Dec 2014 08:37:51 -0800:
The incoming power, at least at the BX cable coming into the furnace,
is not reversed, but, clearly "something" is wrong, so I do
appreciate the advice as to what to look for.
A few things I did in the meantime, which "may" have changed the
situation is that I opened up all the vents in the house, most
of which had been closed for some reason (almost certainly since
last winter), which means the vent airflow was certainly stifled.
I opened all the suckers:
And all the blowers:
And, I ascertained that there is no V-shaped filter in the top
(left) side of the furnace itself:
This lack of v-shaped filters is apparently normal, as it is
described on the furnace cover sticker, which says:
"Horizontal furnace: Filters are located external of furnace.
Consult installer for location."
Interestingly, since most of the vents were closed, I might assume
the furnace had shut off due to lack of air, but I can't find
what the sticker also says is the "RESET" button:
"Auxiliary limit control may be located on blower housing or
top of furnace. To RESET, push button on control firmly.
Refer to USERS MANUAL for more information. Call qualified
serviceman if failure continues."
Also, the sticker talks about a "fusible link", which I also
haven't found yet:
"This furnace is equipped with a fusible element or manual reset
limit switch in burnder compartment and/or draft diverter to
protect against overheat conditions that can result from
inadequate combustion air supply or blocked vent conditions."
Just in case, I hit all the reset buttons I could find, starting
with the two manual limit switches:
When I press the brown button on the manual limit switch, nothing
happens (I had expected a spring-loaded type of interaction):
I pressed the brown button on the blocked vent tube switch:
There were no buttons on the flame sensor and hot surface igniter,
so, I merely wiggled the wires to ensure they were on snugly:
I suspect this is the backside of the fusible link, which likewise,
I wiggled the wires to ensure they were on tightly:
I also flipped the on-off switch, on the gas valve itself, a few times:
I also wiggled all the wires and connections on the control board:
I'll run another series of tests, and see if any of that made
makolber wrote, on Mon, 22 Dec 2014 10:24:18 -0800:
I had read your suggestion and followed it as much as possible.
There is a flame sensor, and a hot igniter, which are located here:
I don't know yet how to physically 'test' them, but they do not appear
to be damaged. There is absolutely no water, and the ground appears
good but I need to run more tests on ground to be doubly sure.
The good news is that, after wiggling everything and opening all the
vents, and replacing the batteries, I called for heat just now:
First the first time all winter, the igniter lit after the blower
motor ran for a minute or so!
Then, for the first time, the flame and igniter went on:
Then, just the flame went on, for about 10 seconds or so:
This happened three times, in quick succession, and then the furnace
went back to the blinking.
I will post the blinking video separately, as it seems to be
blinking a different code now.
Now that all that went on, it might be time to check the air flow switch.
It will be something after the blower mounted on the air chamber. It is a
switch that will probably show open and when you have air flow it will
close. If it does show open, and never closes when the blower starts up,
you have low air flow. Either the blower is not turning or the switch could
be bad. If it shows open, hook the two wires together and see if the
furnace stays running. Or place your meter across the wires and see if they
stay closed. You can probably go to ground from one of the contacts and one
side will always have voltage and the other one will not. Get on the one
without the voltage and see if it ever gets the voltage.
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Stormin Mormon wrote, on Mon, 22 Dec 2014 11:26:40 -0500:
After all the fiddling, I'm finally getting the thermal igniter to
ignite, and the flames go on three times, and then shut off, so,
that's a partial success, I guess.
First, the LED was solid red for a minute or so:
But then, it quickly switched to what appeared to be a code #12:
Then, the flames went on three times and then off within seconds
with a resulting LED blinking code of what appears to be #34:
Given all those inconsistencies within the span of 15 minutes,
I'm not sure if things are changing or if there are more than
one problem or if the thing just needs to settle down, because
those blink codes are changing depending on what is happening
with the blower.
The gas valve is definitely turned on, and there is plenty of
gas on the stove and in the 500 gallon propane tank.
I will doublecheck that the metal case is grounded, and, I will
sand or steel wool the flame sensor and check the amperage if my
Fluke 75 can get down that low.
34: Ignition proving failure: Control will try three more times
before a lockout #14 occurs. If flame signal lost after trial
for ignition period, blower will come on for 90-second
recycle delay. Check for:
- Oxide buildup on flame sensor (clean with fine sandpaper)
- Proper flame sense microamps (0.5microamps DC minimum)
- Gas valve turned off (manual shutoff valve, low inlet gas pressure)
- Green wire MUST be connected to furnace sheet metal
- Inadequate flame carryover or rough ignition
14: Ignition Lockout: Control will auto-reset after three hours.
Refer to #34.
12: Blower on after power up: (115V or 24V) Blower runs for 90
seconds, if unit is powered up during a call for heat
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