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Old 05-05-2021, 06:16 AM   #1
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Furnace quits after lighting

Last night the low was 40 so I set the LP heater to come on around 60 degrees.

The furnace starts, lights and I can hear it roar when the flame lights. It runs for 5 to 10 seconds and I hear it go out. After another 10 secs or so it does it again.starts runs and goes out.

Outside at the exhausts I can feel hot air when it lights then not so hot air until it relites. After the second attempt it can only be restarted by turning the system off at the thermostat for a minute or two.

We have a full tank of propane and Iíve confirmed itís flowing. We used the furnace a lot on a trip in Jan/Feb. since then weíve not been on any trips that needed heat.

We used the heat pump last night but we are going to a dry camping spot today for three nights.

I figure itís either a obstruction in the exhaust or intact. Hoping itís not a igniter/flame sensor as repair right now would be hard to arrange.
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Old 05-05-2021, 07:08 AM   #2
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Assuming is dangerous but here goes!
Assssuming it is a Suburban furnace, this flow chart would be my guide:
https://manuals.heartlandowners.org/...11-05-2015.pdf

Page 30-31 sound like where you have gotten to and that makes you past most of the troubles we find with air retriction, igniter and gas valve problems.
So Simple, right? Or totally bad!

But it does cut the chase a bunch as this snip shows. You have it all working but it thing goes out, so that can be a bad thermostat at best as they are easier to replace or bad board, at least that is what they imply.

So to cut out the chance of the thermostat being bad, can you find the wires for heater from your brand thermostat and connect the two together to test if the fire stays on?

If not the flow chart says bad board but I do not jump that way so quickly as loose wires can also show up as bad boards. The board may be making the right decision but if the wire is loose and doesn't pass that signal we get the same result.

One way a bad board or loose connection might show up is when the furnace begins to heat, the parts shift as they warm, so both a bad board or a loose wire may change at that time.

I suggest check the thermostat, verify tight wires if possible to reach and see if you get lucky?
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Old 05-05-2021, 07:34 AM   #3
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It is a suburban furnace. And it’s accessed from up underneath the rear cap.

As I understand it the igniter is also the flame sensor. The thermostat calls for heat, the propane begins to flow, the igniter lites the burners. I have all that. Then the flame sensor has to heat up and recognize that ignition has taken place. If it doesn’t recognize the ignition it turns off the propane. It will try this routine twice then it turns off at the thermostat and won’t try again until it is reset.

There is also a sail switch which confirms airflow. But I feel I have that or it wouldn’t make it to ignition.

If the air intake or exhaust are obstructed it may cause the furnace to shut down. But I also doubt this is my issue.

It can be a circuit board but that will be a more complicated troubleshoot and part sourcing. So I’m not going there yet.

Listening to the thermostat and the furnace I don’t think that it is turning off the gas at the heater.
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Old 05-05-2021, 08:24 AM   #4
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If the thermostat is defective it may not make any sound but just move in a way that cuts the circuit. This is thinking of something like a small crack in a connection on the thermostat board. Something so small that is can only be seen under a scope but just enough movement to go open. That is where putting a wire between the two wires from the thermostat to the furnace does away with the question.

Can you pull the cover to see a brand and model of the thermostat? Knowing that, one could likely find the two wires that call for heat and then you could just hold a wire loop on those spots on the thermostat, once the fire light and see if it then stays lit. The difference being that it is then a manual operation, done by you, rather than the circuits in the t-stat, which is what you want to eliminate as a possible cause. Since the T-stat is very low voltage in most RV, it can be totally safe and often very easy, once we find which wires do the heating.
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Old 05-05-2021, 08:54 AM   #5
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I would doubt that it the thermostat. It is making and starting the blower/lighting sequence but something in that system isn't sensing that it is firing and shuts it off.

I would see if you can get to the burner and its flame sensor. On small portable LP heaters it is just a thermocouple that if it gets bent wrong, won't register heat and it causes this problem. So check its alignment with the flame. The other issue may be the flame itself. Maybe the burner is dirty and the flame isn't reaching the sensor.

Try these things first before you assume it is an electronics board. From everything you have reported so far it sounds like the flame sensor isn't seeing the flame.

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Old 05-05-2021, 03:03 PM   #6
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Try cleaning your wire connections; and FYI... I saw this one video where the tech found a plug that was not fitted right. Problem solved.

The picture below will show you were this RV had a bad connection. (See Video for whole story.)



Your location is different, but I would think the Suburban "way" is the same.

Good luck.
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Old 05-05-2021, 04:02 PM   #7
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Unfortunately while I can remove the license plate cover and see the furnace behind it, to work on the furnace you have to crawl underneath the RV and drop the entire thing out from below. On a trip like this we have a strict schedule. Oh we'll be in one place for a few days here and there to get things worked on but we going from the RV Deserted BIG City to the very rural boonies.

The nearest RV place from us now is over an hour away. And, we leave here for rural Wisconsin and after that scenic Door County, WI and then the Upper Peninsula of Michigan.

But I'll see if I can get it looked at while we're in Wisconsin. If I were at home I'd tackle it myself. But I'm not prepared for this level of DIY on the road.
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Old 05-05-2021, 04:09 PM   #8
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Richard, I can hear the Tstat call for heat and then it clicks and reacts when the furnace shuts down. I really don't see this as a thermostat problem. If nothing was happening then yes maybe but its the furnace that shuts down the process not the Tstat.
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Old 05-05-2021, 04:35 PM   #9
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Yes, understand the value of being where we can do things. I was suggesting the thermostat as being easier to get too than the real work of pulling the whole thing out.
I might suggest a board but that is one that I know gets into all kinds of fun things we want to avoid!

But before giving too easy, let me throw in some guessing without any knowledge of your RV! Looking at drawings can certainly be misleading but I see a furnace access panel in the parts, so will stick my head out to question if you might be missing what you are seeing? Okay to hit me in the head, if wrong, but it sure would save grief if you could access from the rear as shown. Just looking for a better result than a week without much heat but also willing to be declared totally wrong!

Does it match this manual?
https://manuals.heartlandowners.org/...11-05-2015.pdf
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Old 05-05-2021, 10:59 PM   #10
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Attached is the Suburban manual for all heater types. See page 26-27 for help troubleshooting.

Note: It seems to me these systems are "born to run" and everything else is a safety switch. I.e., a N.C. switch you can bypass to isolate the part. ...The point being, if you take the safety switch out of the circuit, and your furnace works, then you just found your problem.

And I have found that if you know which pin is ground, you can always add an additional ground wire vs. finding the bad ground source.

The flow chart below seems to start with checking the sail switch.

IDK, but I would like to know, can remove the switch and check for continuity or resistance? ...And/or can you physically tie the switch down with copper wire to make sure it maintains a solid contact?

What is inside the sail switch?
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Old 05-06-2021, 08:02 AM   #11
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To my great surprise... the furnace started working on propane last night. We had the generator running with the heat pump heating until bedtime. We turned off the generator for the night and the gas furnace took over and started pumping out heat.

Yesterday, when this issue popped up my first thought was that I had just had the propane refilled a day or two before we left. The attendant fooled around with the propane valve trying to turn it off for filling. Then he turned it on and said it was done. But I checked and it was off.

So, of course, Monday night when it wouldn't run the first thing I checked was the propane valve. It was definitely ON. But I still have propane flow in my mind as an issue. I lit the propane burner and it seemed fine.

Yesterday, in our dry-camping spot I turned on the LP Water Heater and it also ran fine.

So, something made the LP Furnace start again. But what? Gas flow? An intermittent issue with the furnace? I don't know what it is but it's heating me right now and it's 43 degrees outside so I'm taking it.
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Old 05-06-2021, 09:32 AM   #12
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If any of your heat vents are blocked with a sock a towel or any type of cloth it will cause a back pressure and will cause the same problem. Maybe someone picked up some clothing off of on of the vents last night and thats why its working. This happen to me with my Big Horn 5th wheel trailer and drove me crazy. Check all you heat vents. Good Luck.
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Old 05-06-2021, 10:35 AM   #13
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Good advice. Restrictions on either the exhaust or intake ports (wasps) can cause problems.

The flow chart above also talks about replacing the Time Delay Relay, but I would clean the contacts first.

...and I suppose it would hurt to "tap" or "wrap" on the gas valve if you loose your flame again... to see if it starts working of course, and then you found your source.

On the road again...

Having a heater is one thing, but going without hot water for 2+ days is far worse IMO.

Glamping... You never know what a simple luxury is until you own an RV and you have to do without heat or water for a few days.
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Old 05-06-2021, 10:45 AM   #14
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What's inside the sail switch?
Not much more than the contacts and a spring to keep it in one position until the sail level moves it to closed.
Called a sail switch instead of micro switch due to it having a big "sail" to catch the wind??
For a "make-do" I would look at a simple jumper wire to tie the two leads together is that was the only option.

But keep in mind it is not always a good idea to wire around the safety features. If the sail switch is wired down and for some reason the burner does light off as it should, you may fill the RV with gas and THEN if it gets lit, you are in BIG trouble!

I would not expect a blocked vent to make the fire shut down until it reached a very high internal temp to avoid fires as the interior air flow is separate from the combustion air flow. The sail switch checks the combustion air flow and is not involved in the room air flow.

Why is may have changed? The gremlins are big into making us wonder on things like that!! Some quick things that do happen a lot are loose wires that make one day and not the next, small cracks on the board component solder joints can move just enough, sometimes even just a change in outside temp will change things. Back when components on boards were big enough to see, it was sometimes just good practice to run a hot iron over a bunch of solder joints as a quick way to cut that questions out. Now it is just easier to change the whole board and charge the customer because you sure can't see the connections well enough.

Maybe a fellow not sure of what he was doing helped get an air bubble in the propane line, that left you thinking it was enough to light but not enough to burn long term?
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Old 05-06-2021, 10:51 AM   #15
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Nothing on a register... there are only 4 maybe 5 registers and since we don't leave stuff lying around on the floor it's highly unlikely in this case.

It's working normally now. My wife and I are trying to guess and the only thing that changed between Tuesday night and Wednesday night was 147 miles of driving on broken I-55 miles from Bloomington to Chicago.
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Old 05-06-2021, 12:14 PM   #16
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For the folks who want to know more about microswitches or as they are used here, sail switches, I came across this video that really shows all the parts we find on the sail switch plus more. We often only need two connections on our sail switch and it is cheaper to make them so ignore the third connection as in the video and assume our contacts are wired to make the connection when the sail moves.



A good point to know if you get into needing to change the sail switch is that you can use one with three connections just as well as two---IF you are able to move the "sail" off the old to the new. Just leave the third connection open/ignored and use the COM and N/O (normally open) connections.
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Old 05-06-2021, 12:51 PM   #17
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Morich: Great video. It's now part of my tech library for the day I need to diagnose my Suburban Sail Switch.

creativepart: Maybe the road vibrations freed up a gas valve? ...Or temperature is a factor like Morich suggested. Last year I fixed a VDC air-tank pressure gauge by reflowing the "cold" (cracked) solder joints."

No worries. It's now on your watch list.
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Old 05-07-2021, 05:42 PM   #18
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This other thread addresses how another member handled this Suburban furnace problem, and it includes additional helpful comments from Morich.

https://www.winnieowners.com/forums/...ml#post3894436

Who knew there as such as think as a Suburban Furnace Tune-up Kit? ($145 includes a number of parts from PDX Parts in Portland.) This may be just the ticked for us owners who haven't done a thing to clean their furnace in 12+ years.
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Old 05-08-2021, 11:43 AM   #19
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Update: the furnace worked normally for the past four days. Whatever the problem was it’s not evident now.
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Old 05-09-2021, 10:37 PM   #20
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If you had a lot of rain prior to the problem, it could be moisture on the board. After drying out the problem will go away. Sometime a hairdryer can be used to dry them out. I keep a spare board for this reason and raised my board up some to keep water from getting to it.
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