Stormin Mormon wrote, on Mon, 22 Dec 2014 11:26:40 -0500:
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.
Partial success!
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:
https://www.flickr.com/photos/98287134@N02/16082030575/
But then, it quickly switched to what appeared to be a code #12:
https://www.flickr.com/photos/98287134@N02/16081998125/
Then, the flames went on three times and then off within seconds
with a resulting LED blinking code of what appears to be #34:
https://www.flickr.com/photos/98287134@N02/16081950225/
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.
https://c4.staticflickr.com/8/7505/1...4f42e6c5_c.jpg
The gas valve is definitely turned on, and there is plenty of
gas on the stove and in the 500 gallon propane tank.
https://c4.staticflickr.com/8/7508/1...4311f464_k.jpg
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 failu 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
(R-W closed).
https://c4.staticflickr.com/8/7545/1...d3f7f629_c.jpg