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QUESTION:If you don't know how RV furnaces work, or don't care, you probably want to
skip this post.
I have an annoying problem with my fifth-wheel's furnace. I would
appreciate some good advice on how to fix the problem, described below. I
don't know what you need to know to tell me how to fix it, so rather than
spend four days trading terse posts, I think I'll be a little wordy, and get
it over with as quickly as possible.
A little less than a year ago, I purchased an '83 fifth-wheel, and I believe
it contains the original furnace. To the best of my knowledge, the furnace
is a Suburban, and for all I know has never had any maintenance done on it.
Lets get right down to the real nitty-gritty. The problem is in the
spark-ignition sub-system. I'll briefly describe the sub-system's
construction in this paragraph, and the problem in the next paragraph. The
spark-ignition-electrode-rod is mounted in a position such that the tip is
about half an inch above the burner. The burner is "grounded" in the spark
circuit, so the "electrode-tip-and-burner-in-close-proximity" forms the
spark-gap. Normally, at furnace start-up, when the high voltage is applied,
a spark jumps the half-inch air-gap between the electrode-tip and the
burner, which ignites the gas flowing from the burner orifices. In this
furnace, this sub-system works quite well ... for a few weeks.
Here's the problem; during normal operation, over a period of time, let's
say two weeks, a small carbon-soot "bridge" forms or "builds up" between the
electrode-tip and the burner. After a few hundred furnace-start-cycles, the
spark-gap is completely bridged by this carbon-soot build-up. The
high-voltage circuit continues working normally, but, with no air-gap, there
can be no spark. The would-be-spark-current is merely shunted through the
carbon-soot bridge. Of course, no spark means no flame. The failure to
flame means I'm one unhappy (frosty) camper. Of course, to get it to "spark
again", all I have to do is disassemble the spark-ignitor and clean away the
carbon-soot bridge from the spark-gap. But, it's a bleak prospect to own a
furnace that has to be partially-disassembled to clean its spark-ignitor
every few hundred furnace-starts. I've had to do it twice in the last two
weeks. There's no acceptable future in that scenario.
Does anyone have any suggestions on how to fix this problem? I hope there's
a relatively easy answer/fix, like "The coating on the electrode-rod is
obviously burned-off, just replace it", or "it just needs an adjustment,
carefully bend the wire [this way or that way]", or somesuch.
If it's not so simple, just lay it on me; feel free to suggest just about
anything that is sensible, safe, and inexpensive. I wouldn't even give one
of the engineering-types a hard time for suggesting something like, "Oh,
that's easy, just use [some-obscure-but-easily-obtainable-cheap-alloy] as
the electrode rod, because thermal shock, (or radically-different
co-efficients of linear expansion, or whatever), will cause the carbon to
shed from the surface as fast as it collects, and, by the way, [here's]
where you can order it". Something like that would be a satisfactory
answer, (I know ... I'm dreamin').
ANSWER: This is a little strange- the electrode assembly should have
three "probes". A high voltage (spark), a flame sense, and a ground.
The spark should fire between the spark probe and the ground *on the
electrode assembly*- not the burner. This spark gap should be 1/8
inch. The flame sensor probe just needs to be in the flame- about 1/4
inch from the ground probe. Anyway- to the problem. First- you *really* need to have the
furnace pulled and thoroughly cleaned, but, for now- I would try
taking a good vacuum cleaner ( a good shop vac is ideal) and sucking
out first, the lower outside port (this is the intake), then the
exhaust (the upper port), and last- remove the entire burner plate and
burner, and vacuum that out.
I'm not sure when Suburban switched from the cast iron burner
to stainless steel (I think yours should be stainless), but if it is a
cast iron, you need to clean the burner slots. Use a hacksaw blade-
being careful not to enlarge the slots, just clean them.
If it is stainless, just make sure it is clean- look through
it with a flashlight.
If you actually have a Hydroflame, you can disassemble the
burner (not really easy, but not too hard), and clean the "grid"- this
is made of "non-stainless", and will rust, causing problems like
yours.
While you have the burner out- look at the orifice- you can
see it with a flashlight in the back of the furnace, and at least make
sure it looks clean.
Last- if you do have a cast iron burner, there is an air
adjustment on it- IMO- mostly worthless, but it can be adjust while
the furnace is running.
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