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Subject Author Date
Trane Nat. Vent furnace Dan Kohlman 12-01-2006
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Posted by Dan Kohlman on December 1, 2006, 9:13 am
Greetings:

I am hoping someone can offer me some assistance here. I have a
customer that has a standing pilot Trane furnace. Some time ago it
started failing to light the last burner once the heat exchanger was
hot. The flame will come within about an 1 1/2 inches of the burner on
the spreader. Of course, after a short period there will be a small
explosion and the burner may light. This only happens when the
exchanger is hot, it will work normally when it is cold, and don't
happen all the time.

I replaced the burner assbly, gas valve, adjusted the manifold pressure
above 3.5" and below, I adjusted the air up and down and yet the
problem still presists. I think I could solve the problem by moving the
pilot to the center or restricting the air flowing to the burner, but I
don't want to modify the furnace. I am more interested in finding the
solution. I'm sure it is something simple that I am overlooking. One
thing I haven't done yet was check the reaction time or flow
differences between the Honeywell gas valves and WR that normally comes
with the furnace.

If anyone can help me I will greatly appreciated it and so will my
customer.

Thanks in advance


Posted by jamesgangnc on December 1, 2006, 9:59 am
Certainly sounds like the hot heat exchanger is increasing the exhaust
flow pulling the gas away from the pilot. Is it natural draft?

I would not restrict the airflow. But moving the pilot is a
possibility. But it shouldn't be attempting to relight so soon after
it has run either.

Dan Kohlman wrote:
> Greetings:
>
> I am hoping someone can offer me some assistance here. I have a
> customer that has a standing pilot Trane furnace. Some time ago it
> started failing to light the last burner once the heat exchanger was
> hot. The flame will come within about an 1 1/2 inches of the burner on
> the spreader. Of course, after a short period there will be a small
> explosion and the burner may light. This only happens when the
> exchanger is hot, it will work normally when it is cold, and don't
> happen all the time.
>
> I replaced the burner assbly, gas valve, adjusted the manifold pressure
> above 3.5" and below, I adjusted the air up and down and yet the
> problem still presists. I think I could solve the problem by moving the
> pilot to the center or restricting the air flowing to the burner, but I
> don't want to modify the furnace. I am more interested in finding the
> solution. I'm sure it is something simple that I am overlooking. One
> thing I haven't done yet was check the reaction time or flow
> differences between the Honeywell gas valves and WR that normally comes
> with the furnace.
>
> If anyone can help me I will greatly appreciated it and so will my
> customer.
>
> Thanks in advance


Posted by Dan Kohlman on December 1, 2006, 12:42 pm

jamesgangnc wrote:
> Certainly sounds like the hot heat exchanger is increasing the exhaust
> flow pulling the gas away from the pilot. Is it natural draft?
>
> I would not restrict the airflow. But moving the pilot is a
ion. Regarding relighting too soon, when the customer
sets the stat to over 72, that is when the problem starts. She states
that
if she keeps the stat set at 68 or less, it doesn't happen. Strange! I
have
attempted everything I can think of short of installing a different gas
valve, but
this is only a 10> possibility. But it shouldn't be attempting to
relight so soon after
> it has run either.
>
> Dan Kohlman wrote:
> > Greetings:
> >
> > I am hoping someone can offer me some assistance here. I have a
> > customer that has a standing pilot Trane furnace. Some time ago it
> > started failing to light the last burner once the heat exchanger was
> > hot. The flame will come within about an 1 1/2 inches of the burner on
> > the spreader. Of course, after a short period there will be a small
> > explosion and the burner may light. This only happens when the
> > exchanger is hot, it will work normally when it is cold, and don't
> > happen all the time.
> >
> > I replaced the burner assbly, gas valve, adjusted the manifold pressure
> > above 3.5" and below, I adjusted the air up and down and yet the
> > problem still presists. I think I could solve the problem by moving the
> > pilot to the center or restricting the air flowing to the burner, but I
> > don't want to modify the furnace. I am more interested in finding the
> > solution. I'm sure it is something simple that I am overlooking. One
> > thing I haven't done yet was check the reaction time or flow
> > differences between the Honeywell gas valves and WR that normally comes
> > with the furnace.
> >
> > If anyone can help me I will greatly appreciated it and so will my
> > customer.
> >
> > Thanks in advance

Hi James:
Thanks for your reply. It is a natural draft furnace. I did look to see
if the
heat exchanger was cracked in that segment, but there are no
indications
that is a problem. I hate to modify the furnace to solve a problem if I
can
find the right solution. Regarding relighting too soon, when the
customer
sets the stat to over 72, that is when the problem starts. She states
that
if she keeps the stat set at 68 or less, it doesn't happen. Strange! I
have
attempted everything I can think of short of installing a different gas
valve, but
this is only a 100K furnace and I am using a Honeywell which is
rated up to 350K. If you can think of anything else, I will appreciate
it.
thanks again
dan


Posted by Stormin Mormon on December 1, 2006, 4:20 pm
I havn't worked on any Trane 80 percenters, but have worked on other
brands. The couple things that come to mind are:

1) set the lower setting on the fan limit switch down a couple
degrees, so it blows the HX a bit cooler
2) Pull the flame spreader off, and remove the furthest two burners.
Bump em on the floor a couple times (air intake end towards the
ground) to clear what rust and soot you can. Wire brush the tops of
the last two burners, at least the last couple inches toward the gas
tube. Knock the soot out again.
3) make sure the flame spreader bar is back as far as possible, they
tend to be rusty and sticky

Please let us know how things work out. These can be real hair
pullers.
--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
.



Hi James:
Thanks for your reply. It is a natural draft furnace. I did look to
see
if the
heat exchanger was cracked in that segment, but there are no
indications
that is a problem. I hate to modify the furnace to solve a problem if
I
can
find the right solution. Regarding relighting too soon, when the
customer
sets the stat to over 72, that is when the problem starts. She states
that
if she keeps the stat set at 68 or less, it doesn't happen. Strange! I
have
attempted everything I can think of short of installing a different
gas
valve, but
this is only a 100K furnace and I am using a Honeywell which is
rated up to 350K. If you can think of anything else, I will appreciate
it.
thanks again
dan



Posted by DIMwit on December 1, 2006, 6:03 pm
So Stormy, that means you are bald?

Bob


>I havn't worked on any Trane 80 percenters, but have worked on other
> brands. The couple things that come to mind are:
>
> 1) set the lower setting on the fan limit switch down a couple
> degrees, so it blows the HX a bit cooler
> 2) Pull the flame spreader off, and remove the furthest two burners.
> Bump em on the floor a couple times (air intake end towards the
> ground) to clear what rust and soot you can. Wire brush the tops of
> the last two burners, at least the last couple inches toward the gas
> tube. Knock the soot out again.
> 3) make sure the flame spreader bar is back as far as possible, they
> tend to be rusty and sticky
>
> Please let us know how things work out. These can be real hair
> pullers.
> --
>
> Christopher A. Young
> You can't shout down a troll.
> You have to starve them.
> .
>
>

snipped for sanity



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