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Old 05-01-2016, 07:27 PM   #1
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1979 31' Excella 500
Charlevoix , Michigan
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Gas + Spark = ... No Heat?

Problem: Furnace ignitor sparks, propane in the chamber, but no resulting flame (i.e. no ignition).

Question: Do I have a bad ignitor?

Full Story

We were about to set out on our 1st camping trip of the year and the night before as I was testing all the systems I noticed that the furnace wasn't igniting... The furnace is brand new, never used (this trip would have been the 1st time). It's a Suburban NT-20SQ.

Long story short I ended up taking the whole thing apart at 2am convinced that there was just some secret valve that was in the "off" position that I had to turn on to make the thing come alive. No such luck. Put it all back together and my wife called in reinforcements (man do I love her) to help me at 8am the next morning.

Next morning, we pull the furnace out again, take it all apart and confirm the following:
  1. Propane is reaching the furnace
  2. Propane is passing through the furnace's gas valve with adequate pressure into the chamber
  3. The ignitor is sparking
Despite having the essential components needed for ignition (propane and a spark) the furnace just wouldn't light. It would just go through it's cycle 3 times (open gas valve, spark igniter for 7 seconds, detect no flame, shut gas value) then stop trying (fans stays on to vent propane from chamber).

The only thing that I can guess is that perhaps the spark just isn't big enough... looking at the igniter, the spark is just barely visible. Teeny Tiny.

Before I go and order a replacement part, I wanted to get some advice for anyone else who has experience with these furnaces.
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Old 05-02-2016, 09:05 PM   #2
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1979 31' Excella 500
Charlevoix , Michigan
Join Date: Aug 2014
Posts: 291
Possibly a mal-adjusted electrode

I did a bit of research and I think the problem is that the two arms of the electrode came from the factory too close together (producing too small of a spark to ignite the propane).

I found a service manual for similar suburban furnaces to my NT20-SQ and there's a section on adjusting the electrode:

Click image for larger version

Name:	Suburban Furnace Electrode.jpg
Views:	49
Size:	59.8 KB
ID:	261773

When I inspected my electrode, the arms were 1/32 of an inch of less apart. According this service manual they should only be about 1/8 of an inch apart.

I am going to adjust the electrode arm width and see if the furnace will ignite. I'll report back my findings here.
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Old 08-13-2016, 08:00 PM   #3
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1979 31' Excella 500
Charlevoix , Michigan
Join Date: Aug 2014
Posts: 291
Quote:
Originally Posted by trekerboy View Post
I did a bit of research and I think the problem is that the two arms of the electrode came from the factory too close together (producing too small of a spark to ignite the propane).



I found a service manual for similar suburban furnaces to my NT20-SQ and there's a section on adjusting the electrode:



Attachment 261773



When I inspected my electrode, the arms were 1/32 of an inch of less apart. According this service manual they should only be about 1/8 of an inch apart.



I am going to adjust the electrode arm width and see if the furnace will ignite. I'll report back my findings here.

It worked Fixed.
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