Suburban furnace won't heat

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Pat

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Mar 17, 2005
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1,234
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Payson AZ
For the past two nights I have found my furnace blowing cold.? A couple times I was able to turn it off at the thermostat and turn it back on, and it would heat.? Then I'd wake up hours later to no heat.? One thing the manual says is to try about three times and then go for service.?

I followed the maintenance instructions and took off a couple doors and cleaned the burn area.? The burn door gasket disintegrated, so that has to be replaced.? I see the igniter in there and wonder if that needs to be replaced.? I read the info on the suburbanmfg.com website, which says:
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Question 11
My furnace runs, but it's just blowing cold air. What's wrong?
Answer:
Your furnace is in lock-out or the limit switch has opened and not reset. Lock-out occurs when a problem exists during the trial for ignition. Your dealer or a Suburban service center should be consulted to diagnose this condition.
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I found the lockout switch in the schematics in the manual.? Think I should try to reset it, assuming I can get a replacement gasket?

I can't light the thing to check the flame; although, I now know where the little window is to do that.? Another thing I discovered was that the long tube (burner assembly) inside the burn chamber (cabinet)? is worn on only about 1/2 of the tube.? It's just a roughness instead of the smooth metal of the unburned half.? It looks like the flames don't even get down to the second half.? This may be a low setting because my RV is so small.? Everything else was relatively clean and new looking.? The cabinet had a thin coat of rust dust that I wiped off and one miniscule carbon chip on the floor.? There is no soot at the exhaust outside the coach.

The furnace has run fine for 3 years; although, I've really been using it only two of the last 3 years.? I used a portable heater the first year I had this RV.? It was quieter.

I wonder if I should try to replace the igniter.? The corrosion on the burner assembly was similar to the igniter.? Just a roughness to the metal.? No rust, ashes, carbon, discoloration.

I have the NT-16S furnace.?

--pat

Addendum:  Stove works fine.  There is LPG.  Both the onboard and auxiliary tanks have plenty.  120 and 12v power seems to be working ok. 
 

Bob Buchanan

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Mar 3, 2005
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Philadelphia, PA
Hello Pat:

Pat said:
For the past two nights I have found my furnace blowing cold.?

It may be a faulty "Paddle Switch". The blower turns on first based on the thermostat temp. The wind from the blower then pushes the paddle switch to turn on the ignitor. That way, the iginitor can't fire unless the blower is running.
 

John From Detroit

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Apr 12, 2005
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Davison Michigan
The paddle switch is fairly easy to test. However my guess is the igniter. I've had house furnances where the installer did not know how to set up the iginter and all that was needed was to re-set the points to the proper distance as specified in the instructions.  That was about 30 years ago, far as I know that furnance is still working.

Normal wear and tear can also cause the points to need reseting
 

Bob Flight

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Apr 11, 2005
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Location
Rochester, NY
We have same & on going intermittant problem with our furnace.  The wires that run to the gas valve develop enough corrosion over time that they will not let current pass & the gas valves will not open.  The solution has been to remove each wire (there are 3 going to the valve), spray the wire and the end it slides on too with WD-40 and slide the wire back on.  Pulling each wire on & off a few times helps clean the corrosion away too.  The wires are not easy to reach so a pair of long needle nose pliers will help a lot.

The problem we have had is that the thermostat will call for heat, the furnace will start the fans, the ignition cycle starts, but the burner fails to light.  We traced it to the gas valve not opening because the sound of the valve opening was not present.

Hope tis helps.
 

Gary RV_Wizard

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I'm not familiar with your model of furnace, but since the furnace lights some of the time, a corroded electrical connection sounds like the most likely cause to me.  Or as John suggests, the igniter gap has become worn and needs adjustment.

However, one of your symptoms sounds like it could be low DC voltage and I'm wondering if this problem occurs when you are on shore power?  A furnace that lights initially but later fails to re-light may be running down the batteries to the point where the ignition spark is weak or a corroded connection no longer functions.  The furnace fan draws a lot of power and sometime causes a voltage drop.

An intermittent sail switch failure seems unlikely to me, unless it is the electrical connections on the sail switch. Usually the sail either works or does not.    If you have a VOM or continuity tester, you can easily check the sail switch for proper operation.  Just push the "sail" over by hand and check for electrical conuity through the switch.
 

Jeff

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Our furnace would do what you describe: turn on, heat, turn off gas and go into cool-dpown mode but never shut down. Had it repaired by a dealer who said it was a bad switch. Sorry but I don't remember which.
 

Bob Buchanan

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>> An intermittent sail switch failure seems unlikely to me, unless it is the electrical connections on the sail switch. Usually the sail either works or does not. ? ?If you have a VOM or continuity tester, you can easily check the sail switch for proper operation. ?Just push the "sail" over by hand and check for electrical conuity through the switch.
====
On my first MH in the mid 90's (a Winny Brave), I had the same problem of the furnace blowing cold air - and it was intermittent. After checking the obvious, I took it to the top appliance place in Sacramento. They said it was probably all the electrical stuff mentioned so far in this thread. They cleaned all the connections, checked voltage and such and sent me on my way -- and billed their one hour service charge. That night in Reno it would only blow 20 degree cold air. Upon return to Sacto, they said it must be the electric board. They replaced the board and charged me over $100.00.

I then returned to Reno and late that night it stopped working again. This time I went to a service shop on South Virginia street in Reno. ?The service person's first words after hearing my story was, "Sounds like a bad paddle switch". He found it was sticking due to a build up on the bar holding the sail - plus the sail had become loose - and had nothing to do with the electric. Strictly a mechanical problem. It never failed again while I owned the rig.

Was able to get a return of my money from the first repair place. So though it may be caused by other culprits -- that is why I alway recommend checking the paddle switch first. And as you have indicated, Gary, it is not hard to do.
 

Pat

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Mar 17, 2005
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Payson AZ
Thanks for the info.  I've got my work cut out for me tomorrow.  I'll see if I can find the sail switch and the paddle switch based on the parts listing in the installation and operation manuals.  I don't recall the terms.  The igniter I can find, and it's very easy to replace.  It's a bit corroded. 

The low voltage issue is not entirely out of the question; although, I checked available power, and my gauge panel said 3/4 and on green.  In fact, one of the times I tried running the furnace, and it didn't click to ignite at all was during daylight when the solar panel was doing its recharding job, along with the converter.  I am on shore power.  Also, another reason I thought it might be voltage is that I just filled the batteries last week.  They took more water than usual, even though I fill them every month.  Maybe the AZ heat dried them out more than I thought.  Anyway, sometimes after I fill the batteries, they seem to take a few days to recover.  I had thought to change the fuse, but if the blower works, I assume the fuse is ok.  I have one fuse labeled "furnace."  Two times when I turned the thermostat off, waited a minute or so, and turned it back on, the furnace heated, at least once.  The third time I tried that, during the daylight test, it just never sparked.  There's a click when that igniter is sparking. 

Is LP pouring into this thing while it's running cold?

Today I found some gaskets for the little door to the burn unit.  The gasket that was on there disintegrated.  I'll be getting some replacements and backups Thursday.  The igniter will be more of a challenge, because Suburban refuses to sell directly, and all the dealers and repair houses I called today carry no parts.  The RV supply place that has the one gasket has no other parts, including the entire set of gaskets for the furnace or the igniter.  Suburban is kind of a hassle with their elitist refusal to provide customer service.  I was told by two out of three service sites today that they get annoyed when Suburban gives their names as providers of parts.  Guaranty RV here in Junction City OR had nothing.  Huge place and no parts.

I hope replacing the igniter does the job. 

One other issue I had that I may have forgotten to mention is that the burn tube was corroded only about 1/3 of the way down.  It's as though the fire doesn't even get to the rest of the tube, which looks new.  Does that sound normal?

Thanks.

--pat
 

Karl

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Pat,

The sail switch and paddle switch are one in the same, so don't bother looking for two switches.

The panel gauge you're talking about is next to useless. It indicates battery charge, but what you really want to check is the voltage to the furnace control board. The battery supply goes thru many wires, connectors, fuse(s), etc. until it finally reaches the control board, so checking it at the source (battery) doesn't tell you anything. Go to Radio Shack and get a small VOM, then check at the plug that goes into the control board.

If you're on shore power and your converter is operating properly, you can forget about the batteries being the cause. You may have bad batteries or an overcharge condition that's causing excessive drop in battery fluid level, but that's not what's causing your furnace to be inoperative.

The corrosion area of the burner tube is irrelevant as the flame is not evenly spread along the entire interior, and some areas will get hotter than others. Check for soot or other deposits near the insulator of the ignitor wire which can cause the high voltage spark to be shorting to ground there rather than at the burner. Remove them with a rag, mineral spirits, fine steel wool, etc. Also check the position of the tip of the ignitor. Your manual should have detailed instructions on how to set it properly.

It's highly unlikely that you're dumping raw propane into the furnace. The gas valve will shut off within .8 seconds if a flame is not detected and, after a few tries, will go into full shutdown mode. Unless there's something SERIOUSLY wrong with the valve or control circuit, you shouldn't be concerned about blowing up your rig. Besides, you should be able to smell even a small amount of raw gas. 
 

Jim Dick

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Feb 11, 2005
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Titusville, FL
Pat,

Another possible problem is the circuit board. One of my furnaces had an identical problem, it would heat sometimes and not others. I had the board tested and it worked fine. Continued to have the problem. Had the board retested and it failed immediately. Installed the new board and everything has been fine since. Also be sure you hear the gas valve operating. If it doesn't open you won't get any gas flow. It usually has a distinctive click when it operates.

 

Pat

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Mar 17, 2005
Posts
1,234
Location
Payson AZ
The guy at the RV Store in Springfield OR agreed to order the igniter.  He said it comes with the burner door gasket and the igniter gasket.  I'll check the wire separation before replacing the item.  I also talked with Chinook, who agreed it sounds like the igniter.  I'm glad to know how to find the paddle switch.  I'll check that.  There was very little corrosion or rust or dirt in the furnace.  These days while it's waiting for the new part, I have the doors screwed back on to prevent dust accumulation.  Certainly in the future, I will know how to keep it clean and to check the flame. 

I'm glad to hear that the burner tube is ok.  I have gotten a couple helpful emails from Suburban.  I have heard elsewhere that the system board may be the problem.  If it is, that'll cost more to replace.  I might find it cheaper to buy the Suburban 7 year extended warranty; although, the description is very vague about how much of a repair they actually cover. 

Anyway, this project is moving right along.  I'll be phoning the RV Store to order parts a  couple days before I make the trip in to Springfield.

--pat
 
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