"blueman" wrote in message
...
Newsgroups: alt.home.repair,alt.hvac
Subject: FIXED!!!!!: Furnace blows but does not heat (intermittent
problem)
References:
From: blueman3333
--text follows this line--
blueman3333 writes:
We have a "York Diamond 90" gas-fired furnace that was working well
until today.

There seems to be something wrong with the gas flow/valve, burner, or
sensor.

I can see the electronic ignition element turning white hot, then hear
the gas valve click on, then see the blue gas flames light for a
second or two before sputtering out. This cycle repeats itself several
times until, the system "gives up" (or I guess locks out) at which
point the blower just continues to blow cold air forever and no
further ignition attempts are made. The blower continues to blow even
if I shut off the thermostat

Interestingly, if I cycle off the power (even just for a second or
two), the furnace will start up normally and ignite the burners
properly. The burner will continue to fire for a *couple of minutes*
before blowing out at which point it goes into the (failed) cycle of
trying to relight a couple of times before finally giving up and again
leaving me in the stuck state with the blower blowing cold air.

Sometimes in the cycle of trying to re-light it will burn for a
few seconds before sputtering out. Also, sometimes, I hear the valve
clicking on-and-off a couple of times in rapid succession.

Now the other two gas furnaces are working properly, so I don't think
it is a supply problem. Also, I don't think it is a ventillation problem
because it seems to burn fine for a few minutes with a nice blue flame
before suddenly sputtering out.

When I opened up the bottem panel (overriding the disable switch), I
noticed that after it locked up in the continuous blower position, the
diagnostic LED exhibited a pattern of 8 short (red) flashes -- I believe
this simply indicates that the flame is lost 5 times within a heating
cycle which according to the online manual indicates either:
Low gas pressure (unlikely since other two gas
furnaces in the house work fine, right?)
Faulty gas valve
Dirty or faulty flame sensor
Faulty hot surface igniter (unlikely because the flame does
ignite, right?)
Burner problem

Any idea what might be wrong and how to fix?

Even if this is not a DIY fix, I would like to have some idea of what
the potential problems could be so that I can intelligently engage the
service person and make sure that I am not being taken

Thanks!

No thanks to some of the "pros" here, but I fixed the problem myself.

It was a great learning experience -- I learned a lot about furnace
drainage and controls. Best of all, I didn't have to hire any of those
ARROGANT ASSHOLE types that seem to infest this newsgroup.

Only cost to me was my time -- I didn't asphyxiate
myself, blow up the house, or even break anything! Imagine that a
stupid homeowner can actually fix something without bowing to the gods
of alt.hvac.

In all seriousness, I do want to thank the disgruntled alt.hvac pros
because without their bull****, I might actually have given up and
called a tech. But they offered a challenge that I just couldn't
refuse.

So, please if you are a handy homeowner, don't be scared off by these
nitwits. HVAC repair is far from rocket science -- just a little basic
plumbing and electricity. Now to tell the truth, I would probably
never take apart a gas connection because that stuff (along with
roofing) actually scares me, but the rest is easy -- I mean I was
building more complicated electrical control circuits back in grade
school. Just remember that the only reason they bark so loud is that
they are afraid you may actually look inside an HVAC unit and realize
how simple it is and then you may realize that they are just a bunch
of overpaid and overpampered high school graduates (if that).

Anyway, enough of the gloat.
Here are the details of what I believe went wrong and what I did to
fix it in case someone else has a similar problem in the future...

Issue ended up being a problem with condensate drainage (thanks
Dmitrios for the hint based on your experience). The actual cause of it
shutting off was that the inducer pressure switch was triggered
(thanks Tony Hwang).

It Really ended up being two contributing problems. First, the flexible
rubber condensate tube leading from the exhaust side of the ventor
motor to the internal trap (black plastic manifold where 3 condensate
drain lines meet before exiting the furnace) was FILLED with particles
-- so much so that the entire line was blocked solid. Some of these
particles had also started to clog the trap. I couldn't believe how
much crap was there!

Interestingly, despite the clog which presumably had been there for a
while, the system still worked until I added the condensate pump last
week. In the installation, the last couple of feet of the flexible
tubing sloped upwards (after dropping about 20 feet). My guess is that
this created a second water trap that aggravated the more proximal
blockage within the furnace.

In any case, I cleaned out all the condensate tubing inside the
furnace and shortened the final stretch of tubing leading to the
condensate pump so that it slopes down almost vertically into the pump
tank.

All works PERFECTLY now -- ran the furnace for about 2 hours straight
and didn't get a hiccup.

Now contrast that satisfying learning experience with what one might
exect calling in a repair man. Based on my experience with the average
quality of technicians today, they probably would have first tried to
replace everything that moved -- e.g., "lets' try a new pressure
switch" or "how about a new ventor motor" etc... This would take at
least two visits since they would of course have to go order and get
the part. After paying for their marked-up parts and labor, it might
actually have worked for a few days or weeks since just replacing the
parts might have shaken things up a bit.. But then the problem
would inevitably recurr since they wouldn't have fixed the right thing
in the first place. Then they would probably come back to the house a
couple of more times, each time replacing a new part or so. Finally,
they would try to convince me to buy a new furnace since they would
then claim that the problem is a common defect with the model with no
solution and since it is out of warrantee the only choice is to
replace the entire furnace... Sigh... I know the story well and have
seen how it ends...



Glad to hear it!