Thought I'd relay my experience with repairing my home heating unit a few
days ago. Maybe it'll help someone else.
Last Friday when I went to sleep, the heat was working. When I woke up a
few hours later, I noticed the house was cool; checked a vent and it was
blowing tepid air. So I went to the furnace (York P2DP downflow) and opened
the panel, and sure enough, no flame to be seen. I shut it off for a few
minutes and then restarted it. The problem was obvious; the ignitor gave
one little bright spark and then sat there. Close examination showed a
tiny break in it.
Called the local mom-and-pop parts dealer; they had a generic in stock. Did
a quick web check and the generic (AF101) seemed to be a good fit for the
furnace, so I ran down and grabbed one. Got the usual caution about not
touching the element, but already knew that. So I bent the wires to use them
as a handhold to move the element into place, finally got the screw started
in the teensy little space available and screwed it down. Then I turned on
There was no noticeable glow from the ignitor. Instead, below the point
where I could see it, something glowed very bright white for a few seconds,
then the ignitor cracked in two. Natch, the store was closed by then.
As the heat dropped in the house, I decided to use a propane torch as an
ignitor for a temporary run of warmth. That worked for a while; the gas
kept shutting on and off, but it worked for a while. Then it no longer
let the gas flow. Oh well, we were warm and tomorrow's another day.
Next day I send the wife for a new ignitor. I wasn't even gonna ask, but
she did and they replaced it free of charge. (That's what I like about
the mom-and-pop shops; unless you're a regular, the big places usually
won't give you the benefit of the doubt.) Brought it home and tested it
outside the furnace; it worked and I installed it.
This time I got a nice bright orange glow. But no gas. So I removed the
access panel and found a light blinking four times. Looked up the controller
number on the web, couldn't find an exact document but did find similar
units that said four flashes was the roll-out switch. That was fine. So
I started blindly following a troubleshooting guide until I found a list
of the flash codes on the controller itself; four flashes actually meant
the limit switch. Checked it and it was indeed bad.
I wiggled it and prodded it and it came back to life temporarily, so we had
heat for the weekend. Got a new one Tuesday and replaced it.
Here's the part many people will be interested to read. Now that the new
limit switch is in there, the gas no longer shuts off and on during a
normal heating cycle, as it did when I was using my torch as the ignitor.
Apparently the switch was touchy enough that it was overcycling the heat.
I'd call that subjective, except that the past few days the temperatures
outside have fallen quite a lot, with a high of about 30 now and a low of
less than zero F. At those times before, the heat used to run almost
continuously; now it cycles almost like it did when it's forty outside,
except less often.
So even if your furnace is working properly, if it's old you might consider
changing the limit switch on principle. Mine was available for just under
$6 on the net, though I paid $10.74 at the mom-and-pop for immediate
gratification. :) I bet this month's heating bills are going to be lower
than they have been for the more temperate months preceding.
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