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Suburban Furnace doesnt ignite


oldjohnt

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I have a Suburban SF 25 Furnace I can NOT get to light and its driving me to drink *&^%$#@

 

Here's what I've tried so far prior to giving up and drinking but that time is getting close lol

 

1) Turn T stat on and raise temp, so it delays then fan runs, gas valve opens (smell gas outside) but it failed to light after a couple tries then locks out and gas valve closed.

 

2) I had a new circuit with onboard ignitor card so I installed it.

 

3) Voltage to furnace is 13.2 as my Solar has batteries in float mode.

 

4) Outside where I can see and hear and smell I turn it on, T stat calls for heat, fan starts, delay, gas valve opens with good loud sharp SNAP and you smell gas out the exhaust BUT SHE DONT IGNITE.

 

5) I plugged a jumper wire onto the HV ignitor and had end to within 1/8 or so from ground and she ticked ticked ticked and threw a small but blue looking teeny spark to ground several times, but it wasn't real bright or real visible but it was sunny... THIS IS NEW BOARD THAT ACTED SAME AS OLD ONE.

 

6) I tested continuity from HV wire end to igniter tip and it was good with no breaks as wire was flexed around.

 

7) YES I have a manual but its troubleshooting isn't much help other then needs a new board.

 

8) The ignitor looks good and clean, I saw no cracks or carbon traces but I didn't remove it so I only saw one side.

 

9) It looks like there's 1/8 or less from ignitor tip to burner, manual shows 1/8 HOW CRITICAL IS THAT DISTANCE????

 

10 ) I figure the sail switch and any limit switches are okay OTHERWISE the gas valve would never open nor would the HV create a spark.

 

Fan runs, gas valve opens, HV ignitor throws a spark (albeit looks weak), get smell of gas out exhaust BUT THE DARN THING REFUSES TO IGNITE. I'm thinking maybe an ignitor problem????????? I guess I can fully remove and inspect and set the 1/8 exact gap but it seems she ought to light the gas that's flowing out the burner grrrrrrrrrrrrrrrrr New board made no difference !!!! I hate to let a machine beat me and take it to the shop but I'm getting maddddddddddddddd lol

 

PS its a single tip ignitor to burner unit.

 

Thanks in advance for any help, need I remove the ignitor tip and inspect and insure 1/8 gap to burner????????????????? That's the only thing I can think to try next

 

A frustrated John T

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John, the first thing I would do is pull the burner and clean up everything I can. It sounds something like the spark rod is a little dirty. The 1/8" gap is normally not real critical, but try to get the gap as close to it as you can. You can also make sure the ground wire has good connections on both ends.

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ITS WORKING YAYYYYYYYYYYYYYYYYYYYYYY

 

Thanks Tom, after I took a nap I went back down and this time fully removed the ignitor assembly and burner so I could get at things. The burner and ignitor tip was already clean, no carbon or dirt or rust etc., and I figured the ground was okay since the control board and gas valve and HV and the blower all worked okay.

 

HOWEVER I noticed the ignitor tip was located near the burner center in a small area where there were no small holes where the gas flowed out. Soooooooooooo I relocated the ignitor tip right in the middle of 4 small gas outlet holes and set it at 1/8 clearance AND SHE FIRED RIGHT UP AND WORKS AFTER NUMEROUS TRIES.

 

THANKS,

 

John T Once again a happy and non frustrated camper, I will need that furnace this January in mid Florida. HOWEVER I'm looking at those "vented" (or at least part power vented, they use a small pipe to the outside for fresh combustion and venting) catalytic heaters as those regular RV furnaces are sooooooooo inefficient..........

 

Power vented Catalytic Heater: http://www.ventedcatheater.com/6.html

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John, if it were me, I would replace the ignition probe now. That is by far the most common thing to fail in an RV furnace. They are not expensive and it can be very difficult to see any flaw in the ceramic, but they do fail. It may have been cleaning of the burner area that helped, but at least as likely is the probe. I have found that it is pretty common for the ceramic to have a microscopic crack that builds up carbon which then shorts out the high voltage providing the spark. If you clean one like this it will usually work for a short time, then fail again. Eventually such cracks open enough that the cleaning don't help, but it usually does correct it at least one or two times.

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Kirk, good idea, they are readily available in the twenty dollar price range so I will order a back up and carry it with me. I already did the same for my Dometic fridge (spare ignitor tip) and I carry spare boards for furnace and fridge and hot water heater. I'm an old "be prepared" boy scout lol

 

It seemed strange the tip was in the center of the burner where there weren't any small gas outlet holes?? Any ideas on that??? The manual doesn't show that much detail but I moved it just a tad (plus maybe got the 1/8 inch more accurate) so it strikes in the middle of where gas holes are surrounding and for now its working fine.

 

Keep cool and/or warm wherever you're currently located. I'm planning to spend some time next summer in Michigan's Upper Peninsula and I fear when I go to Florida late October its gonna be HOT which doesn't suit well for dry camping.

 

Thanks again,

 

John T

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I had the same issue with our Suburban furnace which turned out also to be the ignitor. The way I was able to trouble shoot it was to remove the furnace to alongside the camper on a table and rehook the gas line up using a extension hose. It was obvious the ignitor was not sparking, so I closed the gap and it has worked going on 2 years now.

Greg

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gj hunter,

 

I tried to bench test mine beside the RV to check for the ignitor tip firing, but I couldn't see very good through the flame peep hole so I removed the cover to try it but then the escaping air didn't let the sail switch close so she never attempted to fire. I could have jumped around it but saw where the tip was located so I removed the entire assembly and cleaned and replaced the tip and its location and 1/8 gap and she has worked fine ever since. Still per Kirk's advice and me being an old prepared boy scout I'm ordering a new tip.

 

Thanks for the advice

 

John T

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It seemed strange the tip was in the center of the burner where there weren't any small gas outlet holes?? Any ideas on that???

 

I'm no engineer, but suspect that the lack of holes next to the spark probe is to insure that it lines up with a grounded metal part and not a hole. Since the flame spreads, I don't see any other reason but that is only a guess.

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Kirk,

 

not to beat this topic to death but just for general information and discussion, the entire burner pot is metallic and conductive (especially to a HV spark) but there's an area maybe the size of a dime in the middle absent any gas outlet holes and all I did was relocate the ignitor tip maybe 1/4 inch to one side over the top of the small gas outlet holes versus where it was firing in that what I will call a "gas free dead spot". Maybe it was sparking before but not igniting the gas ???? and it only re tried maybe once then locked out for safety's sake. The ignitor looked clean and free of any cracks or carbon traces (to the eye) but as you noted there may still be microscopic invisible cracks so I'm ordering a spare. All I can say for sure is since I relocated the tip just a tad she has never failed to light after numerous tries yayyyyyyyyyyyyyyyyyyyyyy.

 

The way those RV furnaces suck gas and electricity I'm looking into those forced air vented catalytic heaters (NOT the regular completely non vented) but not before I do a lot of research concerning their safety.

 

I don't wanna be cold in south central Florida in January as it can be a tad cool at times.

 

John T Once again a Happy Camper, despite the 2 grandkids with us this weekend pushing and pulling and opening and turning each and every thing they could get their little hands on in the RV lol

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Kirk,

 

not to beat this topic to death but just for general information and discussion, the entire burner pot is metallic and conductive (especially to a HV spark)

You asked why there were no holes next to the ignition probe. My response was to offer a possible reason, but it was not a justification or anything. Don't over think things because as I stated, I was just guessing. I'm not an engineer, but I did make a living for 40 years making things work properly in spite of the way the engineers designed them. I suspect the same applies here.

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Kirk, fun discussion, thanks for your "guesses" (hey don't feel bad, I'm guessing here also) and advice about the ignitor. Sorry if our tech talk bores others, but were having fun, learning and maybe helping others. I also had to make a ton of RV's work for forty years as either an owner or used RV dealer in spite of how some technicians may have screwed things up lol. It's not so much I question engineering an area absent gas outlet holes (I'm confident there's a sound engineering reason why), but why was the ignitor tip located there of all places?????????????? THATS MY QUESTION, did the previous owner? or some RV technician? install it incorrectly?? darn if I know. However as soon as I relocated it just a tad over where there were gas outlet holes its worked every time. Since its not broke now, I'm NOT gonna fix it anymore lol

 

Best wishes and God Bless Kirk, take care now. Hope we get to visit on one of my Texas RV trips.

 

John T Too long retired engineer and rusty so NO warranty concerning my old engineers guesses, but we all try our level best to help. There are a ton of great technicians and engineers and solar and RV experts here which I appreciate and am glad to help anytime I can.

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