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Old 11-11-2014, 08:43 AM   #1
KenP
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Suburban furnace problem

I have a propane Suburban furnace, Model NT-12SE. The blower works but the burner does not iignite. I have cleaned the igniter and the burner assembly. The igniter sparks when thermostat turned on, but no flame. I have to turn thermostat on and off about 3 times in succession for the burner to light. I have read about a control or circuit board on this forum, that could be a problem. Any thoughts would be greatly appreciated. I am a first time user of this forum. Thanks.
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Old 11-11-2014, 09:06 AM   #2
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Heater

I would check your vent stack for debris. It could be restricted and not letting the flame stay lit.
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Old 11-11-2014, 09:07 AM   #3
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For starters, try setting the thermostat to AUTO and see what happens when you turn the furnace on. If this doesn't work, get back to us and we'll go from there.

And welcome to the forum BTW.
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Old 11-11-2014, 10:26 AM   #4
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Thanks for the quick responses. I have a simple on and off thermostat, no auto. The vents are clear and the igniter sparks. This time, it never did light after numerous tries. I turn on the thermo and it sparks. I turn it off and on within a few seconds. It sparks but no light. However, I went to check the vents right after I turned it on and I could smell gas coming from the exhaust vent. Perhaps a pluged orifice?
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Old 11-11-2014, 12:48 PM   #5
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Time to check the LP supply. Make sure the cylinders are full and turned on. Check the position of the indicator of its a dual tank regulator.

Light the stove to help purge any air. If the stove lights then go back to the heater.

Using a back-up wrench, loosen the gas line at the heater. Turn the propane on and you should get an instant odor of LP. If you don't then it's time to crawl underneath and inspect the gas line. I have seen numerous gas lines smashed between the floor and frame.
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Old 11-11-2014, 03:25 PM   #6
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Thanks Chuckster. The LP tank is on and 1/4 full and the stove has been used so it's time to check the gas supply and the line. I'll let you know how it checks out.

A few weeks ago, the heater wouldn't light. I took out the igniter and burner and cleaned them both. A little emory cloth on the igniter and steel brush/air compressor on the burner. It worked when I tested it but wouldn't when I needed it. As I said, last weekend, I had to turn the thermo on and off a few times and then it would fire up. Once fired, it seemed to cycle on/off okay, but wouldn't light next morning. So, after the on/off thing 3 times it fired. But, today I tries 6-7 times and nothing.
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Old 11-11-2014, 04:34 PM   #7
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Check your battery voltage, it sounds like either a low battery or your converter may not be putting out the correct voltage? You may also check to make sure all the wires are securely connected. Sometimes the factory will use a crimp connector and not "quite" have one of the wires all the way into the crimp terminal.
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Old 11-13-2014, 04:31 PM   #8
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It's not the electric parts as there is plenty of fan and igniter spark. Batteries are full and lines are good. I haven't checked the propane lines yet but, can't imagine it's a problem outside the heater itself because it lights off sometimes. I'll still check the lines and see how difficult it will be to disconnect and remove the heater unit. This is in a Sportsmobile campervan, so things are probably put in there in some order. Hopefully, I can get in to it. if not, it's off to RV repair.

Thanks so much for all the suggestions. I really appreciate it. Ken
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Old 11-16-2014, 11:11 AM   #9
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cover the exhaust!

I read this on another forum. His furnace would not light, as mine. He covered up the exhaust and it lit. I tried that and mine lit, too. I let the ignitor spark once, no light. Then I covered up the external exhaust port, and it lit when the second spark started. What's up with that?
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Old 11-16-2014, 12:12 PM   #10
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The fan starts before the LP is allowed to flow, and there is a sensor of some sort to sense a pressure change (air flow) in the burn chamber. Covering the exhaust ports may cause the presence of a leak (air) to become small enough for the sensor to keep things lit.

Just thinking out loud here. The unit needs to come out, be inspected, and the board tested at this point.
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Old 11-16-2014, 01:58 PM   #11
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I'll be taking it to the shop when I can. We live 200 miles from 'local' RV dealer. I don't want to try and take it out myself, although it looks simple. Disconnect propane line and fugure out how to disconnect wires that lead into the ajoining wall. Not much space to get into. I don't want to make things worse. Thanks so much.
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Old 11-17-2014, 05:20 PM   #12
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Check for power going to the gas valve? I've seen spider webs cause problems with the flow of gas coming out of the orfice causing lite off issues.
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Old 11-18-2014, 05:04 AM   #13
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When I got up this morning, the furnace (Atwood 8500 series) would not light. Yesterday was in the 70s so it had been shut off for some time. This morning in the 30s. I tuned it off and back on several times with same result. Checked propane supply and that valves were on. All good. Finally read this thread and tried holding my hand over the exhaust port and it lit right off. Is this a sign of trouble down the road or a one time thing? This is a near new Montana. Have had zero problems previously.
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Old 11-18-2014, 08:51 AM   #14
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Interesting Barbell! It probably will be a problem down the road unless we can figure out why it works by covering the exhaust. I tried it again yesterday and after it lit (after covering the exhaust 1 time) I turned off the heater and after the fan stopped, turned it back on. It worked 3-4 times this way. After the heater cooled, for only about 5 minutes, it would not light again. I am comtemplating heading to repair shop in a couple days to get it professionaly looked at. I hope they can fix it in a day as I have to drive 200 miles to the shop. I will keep you posted on a solution, if there is one.
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Old 11-18-2014, 09:18 AM   #15
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Ken, If you're planning to drag it to the dealership for repair, you might want to talk to the service manager, explain your travel situation and ask him specifically if he can work you in when you get there so you won't be forced to leave the trailer and make a second trip. I'm sure, if he is aware of the situation and can accommodate you, he will, but if he doesn't know the situation and gets "blind sided" by the request when you get there, he may not be able to help. Hopefully he can get a service tech to work on it when you drive up.
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Old 11-18-2014, 11:26 AM   #16
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Thanks for the thoughts. I do plan to make an appoinment so we don't have to hang around. I'm hoping just a couple hours after I discuss the whole situation. We will go there the day before and get to the shop 1st thing in morning.
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Old 11-19-2014, 07:28 AM   #17
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24 hours later: Temps into the 20s last night and the furnace cycled on and off just like its supposed to. I did lay awake once or twice wondering if it was going to come back on but it is working just fine now. If anyone figures out why, would appreciate hearing.
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Old 11-27-2014, 09:20 AM   #18
KenP
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Fixed

Well folks, all who answered the circuit board, you were correct. It appears the board was receiving signals to turn fan on, ignite the sparker, and open the sail switch. But, it failed to allow the gas valve to open. No one can answer why, when the exhaust vent was covered, it lite. And, I'm not sure how safe that is anyway. When there is a propane appliance problem, get it fixed. No jerry rigging allowed.

PS: the board costs a little less than $200!!
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