I have a Trane XL90 furnace (high effic, two stage) that goes into a fault
condition every once in a while and will not generate heat until reset (a
big pain especially if it happens in the middle of the night). Was
wondering if there are any furnace gurus out there who might be able to
advise me. The fault code displayed means either a grounding or igniter
problem but I have checked both and nothing seems amiss. It sounds then it
may be a controller board problem but I don't wish to replace it on spec as
they want about $500 for the thing. Actually stopping a Trane is pretty
easy in my case

All help appreciated....

Laurie Forbes


--

Might not be hardware problem, but a firmware issue with the board. If
so, bummer pin down...
JR
dweller in the cellar

Laurie Forbes wrote:

I have a Trane XL90 furnace (high effic, two stage) that goes into a fault
condition every once in a while and will not generate heat until reset (a
big pain especially if it happens in the middle of the night). Was
wondering if there are any furnace gurus out there who might be able to
advise me. The fault code displayed means either a grounding or igniter
problem but I have checked both and nothing seems amiss. It sounds then it
may be a controller board problem but I don't wish to replace it on spec as
they want about $500 for the thing. Actually stopping a Trane is pretty
easy in my case

All help appreciated....

Laurie Forbes




--
--------------------------------------------------------------
Home Page: http://www.seanet.com/~jasonrnorth
If you're not the lead dog, the view never changes
Doubt yourself, and the real world will eat you alive
The world doesn't revolve around you, it revolves around me
No skeletons in the closet; just decomposing corpses
--------------------------------------------------------------
Dependence is Vulnerability:
--------------------------------------------------------------
"Open the Pod Bay Doors please, Hal"
"I'm sorry, Dave, I'm afraid I can't do that.."

On Sun, 23 Oct 2005 16:07:42 GMT, "Laurie Forbes"
wrote:

I have a Trane XL90 furnace (high effic, two stage) that goes into a fault
condition every once in a while and will not generate heat until reset (a
big pain especially if it happens in the middle of the night). Was
wondering if there are any furnace gurus out there who might be able to
advise me. The fault code displayed means either a grounding or igniter
problem but I have checked both and nothing seems amiss. It sounds then it
may be a controller board problem but I don't wish to replace it on spec as
they want about $500 for the thing. Actually stopping a Trane is pretty
easy in my case

All help appreciated....

Laurie Forbes

How old is the unit? It might be a warranty issue.

If it has a silicon carbide hot-surface ignitor, go to your local
supply house and get two more - one to replace, and a spare on hand.
Much cheaper than a new control board - but remember that they are as
fragile as porcelain. There's a reason they are shipped in a sturdy
box well packed in foam.

When I last did HVAC full time these were just coming on the market,
and I always had a few on the truck. Now we just put in a new furnace
here that has one, and I need to go get a spare for the house.

The failure mode is for them to crack across the element and work
part of the time - then after a few cycles they get hot and expand a
bit and the crack opens before the gas lights off. You can see the
sparks across the crack. The controller sees the open ignitor and
trips a fault code blinkenlight, and that's one you have to unplug the
furnace to reset.

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

"Bruce L. Bergman" wrote in message
...
On Sun, 23 Oct 2005 16:07:42 GMT, "Laurie Forbes"
wrote:

I have a Trane XL90 furnace (high effic, two stage) that goes into a fault
condition every once in a while and will not generate heat until reset (a
big pain especially if it happens in the middle of the night). Was
wondering if there are any furnace gurus out there who might be able to
advise me. The fault code displayed means either a grounding or igniter
problem but I have checked both and nothing seems amiss. It sounds then
it
may be a controller board problem but I don't wish to replace it on spec
as
they want about $500 for the thing. Actually stopping a Trane is pretty
easy in my case

All help appreciated....

Laurie Forbes

How old is the unit? It might be a warranty issue.

Off waranty unfortunately.


If it has a silicon carbide hot-surface ignitor, go to your local
supply house and get two more - one to replace, and a spare on hand.
Much cheaper than a new control board - but remember that they are as
fragile as porcelain. There's a reason they are shipped in a sturdy
box well packed in foam.

When I last did HVAC full time these were just coming on the market,
and I always had a few on the truck. Now we just put in a new furnace
here that has one, and I need to go get a spare for the house.

The failure mode is for them to crack across the element and work
part of the time - then after a few cycles they get hot and expand a
bit and the crack opens before the gas lights off. You can see the
sparks across the crack. The controller sees the open ignitor and
trips a fault code blinkenlight, and that's one you have to unplug the
furnace to reset.

Thanks for the suggestion Bruce - sounds like it might be worth a try.
I've been able to watch it once or twice when it faults and the condition
occures just before the ignitor is supposed to heat up. OTOH however, I
measured the ignitor resistance and it showed in the normal range. Are
there any precautions to replacing the ignitor other than fragility?

I just wish the dang fault codes were more explicit - at least then I could
tell if it's a grounding *or* ignitor problem. I've checked the grounding
all the way back and even ran an extra ground wire directly from the panel
to the furnace - no improvement. A furnace guy here told me I might have to
install a separate ground rod for the furnace but I find it hard to figure
out why that would help if it's grounded properly to begin with.

One other thing I've noticed is that it has trouble starting once in a while
in that the inducer blower has to cycle two or three times before the flame
kicks in. It does this even in calm wind conditions. If it does not
succeed in three tries, it quits and gives a code but this has happened only
once since I installed it (in Sept 2000).

Laurie Forbes

Laurie Forbes wrote:

I have a Trane XL90 furnace (high effic, two stage) that goes into a fault
condition every once in a while and will not generate heat until reset (a
big pain especially if it happens in the middle of the night). Was
wondering if there are any furnace gurus out there who might be able to
advise me. The fault code displayed means either a grounding or igniter
problem but I have checked both and nothing seems amiss. It sounds then it
may be a controller board problem but I don't wish to replace it on spec as
they want about $500 for the thing. Actually stopping a Trane is pretty
easy in my case

All help appreciated....

Laurie Forbes

--

Before you spring for a control board check the flame sensor. Modern
glow plug ignited furnaces don't use a thermocouple for flame sensing as
was done in the older standing pilot scheme. There should be a short
metal probe that is placed so one of the burner flames is in close
proximity, a circuit on the control board senses it's resistance to
ground which will change in the presence or absence of flame. These
tend to get a light coating of dirt on them over time and will hold out
the gas valve.

With the power to the furnace off (you'll probably have to cycle the
power anyway to clear the fault condition) remove the access panel
adjacent to the burners and look for a small, maybe 1/8" stainless steel
appearing rod near one of the burners. Wipe it off with a soft cloth or
paper towel. In a pinch just rubbing it with you fingers will probably
do the trick.

On one of our furnaces (American Standard) I have to do this about once
a heating season. This failure is characterized by the blower fan
running continuously, but no heat. If I watch the start cycle the
forced draft fan runs, the igniter comes on, the burner lights but then
goes off. It tries to light three times then gives up and generates an
error code. If the sensor fails after a successful start cycle the
burner shuts down and the blower continues to run. Killing the power,
wiping off the sensor, and turning the power back on solves the problem
for maybe a year or so. My furnace guy gave me a replacement sensor but
as it's so easy to clean and usually happens in the middle of the night
I have not replaced it yet.

This seems to be a common problem and is easy to fix in the above
manner. There are other failure modes in newer electronic controlled
furnaces, if in doubt call your furnace guy.

Paul

--
-----------------------------------------
It's a Linux world....well, it oughta be.
-----------------------------------------

"Paul Batozech" wrote in message
...
Laurie Forbes wrote:

I have a Trane XL90 furnace (high effic, two stage) that goes into a
fault
condition every once in a while and will not generate heat until reset (a
big pain especially if it happens in the middle of the night). Was
wondering if there are any furnace gurus out there who might be able to
advise me. The fault code displayed means either a grounding or igniter
problem but I have checked both and nothing seems amiss. It sounds then
it
may be a controller board problem but I don't wish to replace it on spec
as
they want about $500 for the thing. Actually stopping a Trane is pretty
easy in my case

All help appreciated....

Laurie Forbes

--

Before you spring for a control board check the flame sensor. Modern
glow plug ignited furnaces don't use a thermocouple for flame sensing as
was done in the older standing pilot scheme. There should be a short
metal probe that is placed so one of the burner flames is in close
proximity, a circuit on the control board senses it's resistance to
ground which will change in the presence or absence of flame. These
tend to get a light coating of dirt on them over time and will hold out
the gas valve.

Thanks Paul but I don't think that's my problem as the furnace does not get
to that stage before the problem occurs. What happens is the inducer starts
and ramps up/down normally, the fault condition then occurs just at the
point the ignitor would normally begin to heat up. At that point, the
inducer stops, the blinkenlight flashes (9 times) and the blower comes on
and stays on.

I think I'll try replacing the ignitor on spec but it may be months before I
know if it has done any good as the furnace can go that long now without a
problem.

Laurie Forbes