I have a Suburban NT-30 furnace that is giving me fits. Before coach went into storage, it worked. Then I got a wasp's nest in the blower. I cleaned that out and it now spins up fine - but won't light.
So, next I inspected and replaced the igniter (it was badly corroded). I can hear it firing, but still no flame.
I next checked the gas valve. I can both hear it opening and a test light shows that both magnets are getting power.
All I can think to do is tear out the plumbing and make sure it is clear - and perhaps check to see that the valve is actually opening. Yes, there is gas and yes, the valve to the furnace is open :)
Does anyone else have any ideas? Thanks!
I put mine on the bench and powered it up. It turned out to be the sail switch wasn't free, was hanging up a bit. I freed that and exercised the gas valves and she woks well now.
According to the information in the manual, the sail switch has to be working for the gas valve to be energized. Therefore, I don't think that is the problem. I am really stumped. Hm?
My valves wouldn't pass air when blown into but a few cycles and they freed up. Blow by mouth or very low pressure.
I know a lot of guys that have valves that pass air, usually at the most inconvenient time too. W%
It's not very nice to make fun of us old folks. W%
Joan, you said exactly what I was thinking too... LOL!
You say you can hear the igniter, but can you see it? On mine there's an inspection window and I can see it sparking when it's working.
If you can't SEE yours and the gas is OFF, you could safely remove the igniter, leave it connected and place it on something non conductive and preferably non flammable, and verify that the thing IS actually making sparks, and not just noise.
If it is, then the only thing left is the plumbing and/or the valve itself.
Well, I finally recovered enough from most recent back problem to be able to check out the furnace valves. When I put 12v to the valves with a jumper set up they open right up. Tubes are clear too. Next I'll put it back in the coach and see if I can get it to light...... if it doesn't fire up I'll check the igniter for spark.
In any case, I'll post the results......
Further troubles with mine so I benched it and found the grounding wire was bubbling on both sides of the plug. In the interest of safety I replaced it, caught a sale at PPL. EZ swap, no worries now.
I'll be watching with interest to see what you find.
Quote from: DonD on November 15, 2012, 08:39 AM
Further troubles with mine so I benched it and found the grounding wire was bubbling on both sides of the plug.
I assume you are talking about the connection on the valve - correct?
No, the feed, both sides of the plug so I knew it wasn't a bad connection in the plug.
You will not get ignition spark if the sail switch is not engaged so given you are getting spark the sail switch is ok.
Have you purged the air out of your gas lines? Sitting over the winter you usally end up with air in the gas line. First thing is to get the burners on the stove working. This will remove most of the air leaving only the line from the main supply line to the furnace unpurged. Getting the air out of that line may take 20 or more tries depending the length of the line.
An in-depth description of furnace operation: http://www.classicwinnebagos.com/forum/index.php?topic=2640.msg5117#msg5117 (http://www.classicwinnebagos.com/forum/index.php?topic=2640.msg5117#msg5117)
You have a DSI model furnace.
Dave
OK, it's been a while, but we finally solved the problem today.
A few weeks ago, I pulled the furnace and took it apart. I used a battery to cycle the valves a number of times. They opened just fine. So, at a total loss to understand what the problem, I put it back together.
Today we put the furnace back into place and hooked it up. We ran the stove to make sure the gas line was as free of air as we could make it.
Then the big moment: We fired it up. It lit on the first try!!!! :)clap
I can only assume that cycling the valves freed them up.
Thanks to everyone who offered advice!
I need to know more about tis cycling the valves part. My furnace is exactly 2 years old and it wont light. We have spark, lots of propane and no mud dobber nests in it. I cant find the problem anywhere.
Hi MJ, good to see you again.
Take a look at the topic,
"Anatomy of a furnace".
https://www.classicwinnebagos.com/forum/index.php?topic=2640.msg5110#msg5110
This should help.
I did thank you. I need someone that KNOWS furnaces. What I have found is that I can blow through the gas valve IF I power both sides. BUT if I try to blow through it while the electrode is clicking I cant. It seems to be opening for just a second then closing again.
Still no takers on this topic? I changed out the gas valve today after waiting to get it in the mail and still no heat. Everything seems to run perfectly except we get no heat. The fan comes on, the thermocouple starts sparking, no ignition so it goes through the sparking sequence 2 more times and still no ignition. Have run the stove to be sure there is no air in the lines. There is no gas smell from the exhaust. I'm at a total loss as to what to do next.
Here is the service manual for the Suburban furnaces.
http://techsupport.pdxrvwholesale.com/wp-content/uploads/2017/09/Suburban-Dynatrail-Furnace-Model-NT34SP-Service-Manual.pdf
Page 11 has the troubleshooting instructions for electronic ignition models. It seems like your problem may be # 5. Also, on the next page, item C might help you track down the problem.
Thanks, I have done everything except check the gas pressure and the limit switch. I was told that if the limit switch was bad it would shut off AFTER starting. Mine wont even start.
But I am confused about this step: If sparking is audible approximately 15 seconds after the blower starts, but no ignition,
check the high-tension wire for continuity, grounding and secure connections. Repair if
necessary.
If there was a problem with the wire would it still spark?
If the switch has power and good ground, and does that, then the switch is malfunctioning.
If it has power and good ground and it's not even starting, then it's not functioning at all.
Check the ground and that it is, in fact, getting power.
Quote from: Elandan2 on October 28, 2020, 05:09 PM
Here is the service manual for the Suburban furnaces.
http://techsupport.pdxrvwholesale.com/wp-content/uploads/2017/09/Suburban-Dynatrail-Furnace-Model-NT34SP-Service-Manual.pdf
We have these manuals right here too...
Quote from: Oz on October 29, 2020, 02:58 AM
If the switch has power and good ground, and does that, then the switch is malfunctioning.
If it has power and good ground and it's not even starting, then it's not functioning at all.
Check the ground and that it is, in fact, getting power.
Which switch is this? I still have no heat and it's going to be in the 30's this week.
By following the information referred to several times, and your description, you have gas supplied and you have spark. But, it sounds like you have no gas to the spark. This is controlled by the gas valve. If you know there is gas going to the valve, the ignitor is working, but nothing lights, then there must not be anything to light.
Again, referring to the Anatomy of a furnace topic which covers all of this.
https://www.classicwinnebagos.com/forum/index.php?topic=2640.msg5110#msg5110
Dave laid out the process very well. Scroll down to "Blower runs but furnace fails to ignite".
I replaced the gas valve, working on limit switch now, I went through that post and also a bunch of youtube videos and anything else I could find. Just haven't figured out the problem.
There's a 'sail' switch too, which senses that the burn air is moving through the unit. Those are prone to sticking and it won't release gas and try to ignite if that switch doesn't work.
Based on what I have read here, there is a gas delivery issue.
- When turning the Propane system on at the tank, turn the gas on very slowly. There is a safety valve in the propane tank that is used to drastically reduce the flow from the tank to the regulator if it senses a large volume of propane is discharged from the tank. This is safety feature where if the RV is in an accident and the propane lines are ruptured, the gas flow is greatly reduced. If the safety valve is triggered, to reset it, you have to turn the tank supply OFF for 60 seconds and then very slowly open the tank supply valve.
- If the propane system in the RV has been opened up (e.g. furnace removed for service), then it is best to purge most of the air out of the system using the burners on the stove prior to attempting to light the furnace. Even so, it my still take multiple attempts to start the furnace in order to purge the air from the furnace gas lines
- Gas nozzle is clogged up not allowing gas into the combustion chamber. Use compressed air to clear out. Best not to use any sort tool to clear it as it could increase hole size resulting in to much gas into combustion chamber. Replace nozzle if not able to clear.
- Oil from propane can build up in supply lines resulting in clogged lines and valves. Maybe able to clear with compressed air, otherwise, replace lines.
Please note:
You would NOT get ignitor spark if:
- Limit switch was open
- Sail switch was not operating properly
Thank you Dave, we know about the safety on the propane bottle. We have run the burners on the stove to purge air. You may be on to something with the gas lines maybe being clogged. The lines in the furnace are ok, we did blow through those. BUT maybe there is a problem between the bottle and the furnace. Now to go blow air through that one. Will update if it worked.
Well, I thought you could be on to something until I got in there and realized my supply line also supplies my wave 6 heater and it runs fine. And to be clear.. the wave 6 heater is connected to the supply line 1 inch from the furnace connection.
So to summarize: I have spark... Sail switch was checked and working, ignitor/ thermocoupler (whatever its called on this) was replaced, gas valve was replaced, limit switch was ordered( dont believe it's a problem though) No nests or clogs in furnace... Sparks 3 times before going into lock out due to non-start.
Everything seems to work PERFECTLY except that it wont light..
NT-30 Parts Drawing (https://fwwebbimage.fwwebb.com/ProductInfo/071076_Parts_List_Spec.pdf)
Then my only other thought is that the Main Burner Orifice (item 49), Manifold Pipe (item 52), Gas Inlet Pipe (items 54, 57 - 60), or Gas Burner (item 48) is/are clogged up preventing the gas to get through. Spiders love to get in those areas and nest over the summer.
Dang it! Those have all been cleaned and blown out. We have literally gone through everything. We have taken it out about 10 times now. The only other thing we can think of is "gas pressure"
Is there any possible way that the furnace needs more pressure than the wave 6 heater? We did blow through the supply line just to be sure it wasn't partially clogged, (guess it could still be partially clogged) But our only other thought is maybe the pressure regulator on the tank? What do you think? It's going to be 27 degrees here tomorrow night and I dont think the wave 6 heater is going to keep us toasty.
To test the gas pressure you will have to make a DIY Manometer (https://www.youtube.com/watch?v=tWNFVRvbAqw&ab_channel=grayfurnaceman). Manual says your supposed to have 11" Water Column.
The only other thing I can think of is the control board is not sensing the initial lighting however, you indicated that you do not hear/see any evidence of a flame (just hear/see spark) which is why I did not mention it before.
You are correct, I watch the sparking and it never lights.
Here we are a year later and still have no heat.
Recap: Furnace runs but wont light. Sail switch is good, new gas valve, new limit switch.
Now, in all my testing today I found the problem (sort of) If I apply 12 volts to the gas valve (both sides) when the HV wire is creating it's spark then the furnace lights right away.
There is 12v getting to the plug on the side of the furnace (checked and verified).
I spoke with someone at Dinosaur boards and I was told that 12v must get to the gas valve, so I attached my voltmeter to the leads that attach to the gas valve. When the valve "clicks" open the volts jump to about 5-6 volts (happens too fast to see an accurate voltage) then drain down to .09 Volts where it stays until the furnace gives up trying.
I have looked at a price for a new board so I can replace it IF that is the only way. Now I have 2 questions..
#1 Where can I check for my missing voltage? Bad or loose wire or something?
#2 My board doesnt seem to have a connector that you pull off the pins. So I was wondering if anyone has changed one of these and could tell me how you disconnect it.
Do you have the manual for this? It may help a lot. Check in the member area. We have NT furnace manuals.
I have read through the manual, thank you. The manual does state that if there is "no" voltage at the gas valve to replace the board. I do have some voltage but not enough. I just want to be sure that there isn't something I can check before paying over $100 for a new board just to end up with the same problem.
Trace the wire back to the source. Check it before where it connects. If it's good there, you know it's the board.
Lower than anticipated voltages can be caused by the ground side as well. Trace back the ground that is supplied to the board if you haven't done it already.
You said you can open the gas valve with 12v. Rig it up so you can light the burner manually at the appropriate time, and see if it will sense the flame and keep running after you remove your 12v. I bet it shuts off because the board can't keep the valve open.
The board thinks it is turning the valve on, but not detecting a flame, so gives up. The board is satisfied with the order of operations all the way up to flame detection.
Sure seems like it's the board.
You are correct, it does shut down as soon as I remove the 12v to the gas valve. But that still only shows the valve isn't receiving enough power to stay open. I am going to take it back out and trace the ground wire and check for any loose or corroded connections before I order a new board. Mainly because I need to find a part number for the board. And I still don't know how to disconnect the board.
Hello MJ. Sorry to hear you are still fighting this issue. At this point I would agree you have it down to a board problem. Should you decide to replace it I would highly recommend you go with a Dinosaur Electronics Board. Their products are considered to be far better than OEM.
http://www.dinosaurelectronics.com/
They do not sell direct, but provide you with a list of dealers, and prices are comparable or better than OEM. Their Customer Service was excellent when I dealt with them some 3 or so years ago. If you provide them with proper furnace and board info they will tell you exactly what replacement is required.
The board number is usually on the back, board generally fastened with 4 screws into stand – offs on the board.
Wires are generally pin connectors to the board.
Best of luck.
Spot on, thanks, Terry!
Assuming you have a NT-30SP model furnace (Fan Control Module Board), as described below, there should be 12VDC +/- 1VDC applied to the gas valve throughout the entire 7 second ignition cycle period (ignitor running). 7 seconds is plenty of time for a volt meter to read the value. If flame is detected, the board will leave the gas valve ON until thermostat shuts OFF.
Gas valve IS NOT on during Purge cycle.
If the Control Board is bad, Dinosaur is the way to go. Just make sure to get the correct model.
(http://dave78chieftain.com/Furnace/Suburban_NT-SF-SH_Furnace_Service_Manual-24.jpg)
Figure 28: NT30-SP Furnace Wiring Diagram
(http://dave78chieftain.com/Furnace/Suburban_NT-SF-SH_Furnace_Service_Manual-33.jpg)
Thank you Dave, I guess I just need to purchase a new board and try it. The only reason I hesitate is because the gentlemen at Dinosaur Boards said there could be a wiring issue that would cause the voltage drop. Oh well, time to just throw more money at it.
Put your meter across the + and -12v at the (supply) connector and try it. If the voltage stays up, it's not the wiring to the board.
(http://dave78chieftain.com/Furnace/Suburban_NT-SF-SH_Furnace_Service_Manual-33a.jpg)
1. Connect the NEG lead of the voltmeter to a ground point.
2. When the Thermostat is ON, you should have 12VDC +/- 1 VDC at all points labeled as 1 (fan comes ON also)
3. When the fan gets up to speed, the sail switch closes and you should 12VDC +/- 1 VDC at all points labeled as 2 (start purge cycle to evacuate any excess propane in combustion chamber to prevent an explosion)
4. 15 Seconds after you get voltage at 2 , you should get 12VDC +/- 1 VDC at the gas valve (turn ON) and high ignitor voltage (do not measure ignitor voltage) at electrode (7 second ignition cycle).
Warning: do not measure ignitor voltage
Please note that the single letters on the drawing represent wire color (Y=yellow, BL=Blue, BR=Brown, R=Red, G=Green, O=Orange, BK=Black)
The drawing reflects a common grounding point that all components connect to (eg: the yellow ground wire from the gas valve). It also is connected to RV -12VDC.
The gas valve has 2 solenoids in it so the Brown wire from the control board connects in 2 places. Likewise, the yellow ground wire connects in 2 places also.
Dave