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Old 12-13-2013, 08:16 PM   #1
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Suburban NT 30 S Furnace issues

Good evening all. As the cold weather is approaching here in south Georgia, we decided to turn on our furnace. Well, at least one of the two. I have two Suburban NT 30 S furnaces. Neither of them worked. So I pulled both of them out. I checked the dreaded sail switch on both with the ohm meter and found one that is faulty. So I took off the sail switch on one of them and put it on the other. She fired right up. Worked good for about a week (temperatures got down and she kept up). Ran low on propane..about 1/4 tank and she stopped firing. So, I refilled and took the RV back to the camp site. I had to cycle it a few times but it fired up again. In the middle of the night, we woke up and it was freezing inside! The blower was on, but was not coming out hot. I cycled it a few more times and it came back on. Did this a couple times a night for a few nights. It was starting to get old. I took it out again to exercise the valve (thinking it was just stuck). I placed a 12v wire to the front at rear solenoids...hearing them click on and off. Put the furnace back in and reconnected everything, lit on the 2nd attempt. After a few hours of burning it did its normal cycle and cold air starting coming out again. Further investigation showed that the valve wasn't even opening at all. Looks like it went out for good this time. Took the whole furnace out again and tried to put 12 volts to it and nothing. Both solenoids are gone. And are stuck open. Therefore, I do not get a spark. I took out the secondary furnace that I was using as parts to check the solenoids, and the front one clicks with +12v, but the rear does nothing. I take it the rear is shot? We are stuck here (going to be in the 20s on Sunday), and no furnace! We do have the two coleman ac's with heat on them, but cant run both of them because we are on 30 amp service. So we run one of them and it doesn't barely anything at night. Anyways, I know some people have had similar issues with these furnaces. Is there a less expensive way to fix them? ~$70 for a gas valve is crazy (and I don't think that they sell the solenoids separate). Also, my atwood hot water heater takes quite a few times to light. I thought this was a problem with the main propane regulator...and could have been the problem with the furnaces....could a faulty propane regulator blow out the solenoids? I'm unsure about that. Any answers are much appreciated. Just don't know where to go from here. Have two dead furnaces that just need a gas valve / solenoids.

Thank you.
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Old 12-13-2013, 08:20 PM   #2
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What are the ohms on the gas valves?
Is the board putting 12V to the gas valves?

Also, to check LP pressure, you need a manometer, no other way.
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Old 12-13-2013, 10:45 PM   #3
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If the grounds are bad or the batteries are not taking a good charge then the solenoids won't reliably cycle. You may replace the parts and get going for a while however if the root cause is low voltage, bad grounds and such then they will just fail again. Also the gas valve won't open if the ignitor circuit does not provide good feedback about their condition and the resultant flame. As for replacement coils for the valves it depends on the brand and possibly local legislation as there was a push to not provide parts to rebuild gas valves to the consumer the last time I was looking into it however that may have been unique to Massachusetts where I was living at the time.

I believe those valves are made by Maxitrol so a call to one of their dealers may get you access to replacement coils if they are available.

Does the CV200 look about right?
http://www.maxitrol.com/Literature/CV_CC_EN_11.2011.pdf
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Old 12-13-2013, 11:07 PM   #4
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Quote:
Originally Posted by jesilvas View Post
What are the ohms on the gas valves?
Is the board putting 12V to the gas valves?

Also, to check LP pressure, you need a manometer, no other way.


The ohms on the gas valves is 85 ohms. The board is putting 12v to the valves as well. I have yet to check gas pressure. I know it has to be between 11'' - 13'' but haven't bought a manometer yet.
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Old 12-13-2013, 11:11 PM   #5
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Quote:
Originally Posted by NeilV View Post
If the grounds are bad or the batteries are not taking a good charge then the solenoids won't reliably cycle. You may replace the parts and get going for a while however if the root cause is low voltage, bad grounds and such then they will just fail again. Also the gas valve won't open if the ignitor circuit does not provide good feedback about their condition and the resultant flame. As for replacement coils for the valves it depends on the brand and possibly local legislation as there was a push to not provide parts to rebuild gas valves to the consumer the last time I was looking into it however that may have been unique to Massachusetts where I was living at the time.

I believe those valves are made by Maxitrol so a call to one of their dealers may get you access to replacement coils if they are available.

Does the CV200 look about right?
http://www.maxitrol.com/Literature/CV_CC_EN_11.2011.pdf

Checking the voltage everywhere on it, and it is staying at around 12.5 volts. I've even tried shutting off anything that would be connected to the batteries to make sure.
I will look into Maxitrol replacement valves (and coils).

Yes the CV200 looks identical.
I'll check it out some more in the morning.
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Old 12-14-2013, 05:00 AM   #6
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Originally Posted by elstonek View Post
Checking the voltage everywhere on it, and it is staying at around 12.5 volts. I've even tried shutting off anything that would be connected to the batteries to make sure.
I will look into Maxitrol replacement valves (and coils).

Yes the CV200 looks identical.
I'll check it out some more in the morning.
If there is a bad ground or power lead going to the heater then it may still register 12.5 volts until you put a good load on it. Had a similar issue with my water heater and found that when I ran leads directly from a 12 volt battery to power it up everything worked. Traced down the wiring and found a wire nut that had gotten wet and had no dilectric grease in it. Everything has worked just fine after I fixed that one connection some years ago.

How old is your coach anyways? Mine is going on 13 years now.
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Old 12-14-2013, 07:35 AM   #7
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Originally Posted by NeilV View Post
If there is a bad ground or power lead going to the heater then it may still register 12.5 volts until you put a good load on it. Had a similar issue with my water heater and found that when I ran leads directly from a 12 volt battery to power it up everything worked. Traced down the wiring and found a wire nut that had gotten wet and had no dilectric grease in it. Everything has worked just fine after I fixed that one connection some years ago.

How old is your coach anyways? Mine is going on 13 years now.
I'll look in to that as well. Probably going to end up buying a new furnace. This is so frustrating!!!
Its an 86 Allegro.
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Old 12-14-2013, 08:04 AM   #8
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The gas valves test good then that way.
I would do it on a bench if you can. External LP supply, external 12V supply and then see what happens.
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Old 12-14-2013, 12:59 PM   #9
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At 27 years those have been in service quite a while.

They are on sale for $635.57 each with only 2 left in stock:
Suburban NT-30SP RV Furnaces : Amazon.com : Automotive
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Old 12-14-2013, 06:27 PM   #10
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At 27 years those have been in service quite a while.

They are on sale for $635.57 each with only 2 left in stock:
Suburban NT-30SP RV Furnaces : Amazon.com : Automotive
Yeah. Just found someone selling one for 100 bucks on craigslist. And another for 150. Still works well. I know they can be rebuilt. These don't look too old either. I might just have to bite the bullet and get the two on craigslist.
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Old 12-14-2013, 09:37 PM   #11
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Yeah. Just found someone selling one for 100 bucks on craigslist. And another for 150. Still works well. I know they can be rebuilt. These don't look too old either. I might just have to bite the bullet and get the two on craigslist.
Is the Allegro a keeper? If so I might be tempted to just buy the one and rebuild the one you pulled to replace the second unit. Then take the one you have left over and rebuild that one as a spare or sell it as refurbished to cover your costs.

I am having an intermittant issue with my SF42 not firing all the time and will probably be facing pulling it and benching it also. Probably dirty connection or a sticky sail switch. It is interconnected with the Basement Airconditioning duct work and I have not vetted out how entangled that makes things yet even though it appears to be a straight pull out the back of the coach through the access panel.

My Adventurer is also only 30 amps however it is insulated well enough that 2 electric heaters on low (15 amps draw combined) takes care of it even when the nights drop well below freezing. Seems it was originally ordered for a film crew shooting video of Alaska. I put a small wall hung Sunbeam in the salon and a small heat fan in the bedroom and thats all it takesn to keep it toasty warm. Was not paying attention and had it up to 78 with them on low. The Sunbeam has a thermostat that has 5 degree steps while the heat fan just has an automotive hotter and colder knob so you have to guess and I guessed wrong one night. I really don't like having to do $50+ propane fillups so I use the electrics whenever possible.

Amazon.com - SUNBEAM Fan Heater, 1 Touch Electric Thermostat, alci Plug - Space Heaters
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Old 12-15-2013, 08:10 AM   #12
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Is the Allegro a keeper? If so I might be tempted to just buy the one and rebuild the one you pulled to replace the second unit. Then take the one you have left over and rebuild that one as a spare or sell it as refurbished to cover your costs.

I am having an intermittant issue with my SF42 not firing all the time and will probably be facing pulling it and benching it also. Probably dirty connection or a sticky sail switch. It is interconnected with the Basement Airconditioning duct work and I have not vetted out how entangled that makes things yet even though it appears to be a straight pull out the back of the coach through the access panel.

My Adventurer is also only 30 amps however it is insulated well enough that 2 electric heaters on low (15 amps draw combined) takes care of it even when the nights drop well below freezing. Seems it was originally ordered for a film crew shooting video of Alaska. I put a small wall hung Sunbeam in the salon and a small heat fan in the bedroom and thats all it takesn to keep it toasty warm. Was not paying attention and had it up to 78 with them on low. The Sunbeam has a thermostat that has 5 degree steps while the heat fan just has an automotive hotter and colder knob so you have to guess and I guessed wrong one night. I really don't like having to do $50+ propane fillups so I use the electrics whenever possible.

Amazon.com - SUNBEAM Fan Heater, 1 Touch Electric Thermostat, alci Plug - Space Heaters

The Allegro is a keeper. She runs great after some tune up, and everything works now (except for the furnaces...which would work before). We are using her for our family now. We left our cushy life near the beaches of Florida to move into this and head out west to build an off the grid community; For the homeless, and for everyone else who wants to switch to alternative energy and / or being semi off the grid. Of course in the interim we still need propane and gas to get there, but everything has been so costly lately. Just needing a couple good furnaces to keep us warm at night! A company wants to film us making this transition and building these communities.
Where are you located? Would sell at a decent price. When she was firing, (one of them) would keep the 35 ft rv warm and cozy all night.
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Old 12-15-2013, 04:12 PM   #13
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If the grounds are bad or the batteries are not taking a good charge then the solenoids won't reliably cycle. You may replace the parts and get going for a while however if the root cause is low voltage, bad grounds and such then they will just fail again. Also the gas valve won't open if the ignitor circuit does not provide good feedback about their condition and the resultant flame. As for replacement coils for the valves it depends on the brand and possibly local legislation as there was a push to not provide parts to rebuild gas valves to the consumer the last time I was looking into it however that may have been unique to Massachusetts where I was living at the time.

I believe those valves are made by Maxitrol so a call to one of their dealers may get you access to replacement coils if they are available.

Does the CV200 look about right?
http://www.maxitrol.com/Literature/CV_CC_EN_11.2011.pdf

***Update: Checked the voltage today. She is running steady at 11.9 while plugged into shore power and the converter box is running (and blower is running). When it tries to ignite, the voltage spikes up to 16v. Is this normal?
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Old 12-15-2013, 04:43 PM   #14
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The converter sounds iffy. It should be a constant 13.5V + or -.5V
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