RV News RVBusiness 2021 Top 10 RVs of the Year, plus 56 additional debuts and must-see units → ×


Reply
 
Thread Tools Display Modes
Old 01-14-2021, 01:13 AM   #1
Junior Member
 
Join Date: Jan 2021
Location: Independence, Mo.
Posts: 2
Troubleshooting my Suburban NT-30SP furnace

I have been fighting with this furnace for days. It will start and will burn for one cycle. It shuts down but the next time it starts it is just the blower motor.....no flame. I checked the electrode assembly and it seems to be fine. I did notice that when it does start, the electrode sparks and when the burner runs, the electrode gets red hot. Is this the electrode still trying to run?
Bear816 is offline   Reply With Quote
Old 01-14-2021, 10:07 AM   #2
Senior Member
 
SeaDog's Avatar
 
Join Date: Jan 2016
Location: Idaho
Posts: 8,316
Welcome to the forum its a great place to get your questions answered. That electrode getting red is part of the flame proving circuit.
__________________
Retired Navy
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho
SeaDog is offline   Reply With Quote
Old 01-14-2021, 01:26 PM   #3
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 10,916
Sounds like an intermittent problem. Most common of these is the Sail Switch.

Might need to see if the furnace has had a lot of pet hair or dust sucked into the inside air intake.
__________________
"A wise man can change his mind. A fool never will."

"You only grow old when you run out of new things to do"

2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan
TitanMike is online now   Reply With Quote
Old 01-14-2021, 02:02 PM   #4
Senior Member
 
Join Date: Jun 2013
Posts: 887
there should be a LED on the circuit board that blinks a code for why it shut down. I'd suspect a sail switch or circuit board, most common problems I've read about. Has this just occurred or has it been a problem in the past. Some furnaces are incorrectly ducted and don't get enough air across the heat exchanger and fail on high limit. Put a meat thermometer in the supply duct next time and see if the burner is shutting off before it reaches temperature.
nayther is offline   Reply With Quote
Old 01-14-2021, 05:45 PM   #5
Junior Member
 
Join Date: Jan 2021
Location: Independence, Mo.
Posts: 2
Unfortunately I do not have a history for anything on the motorhome. I just purchased a few months ago knowing it was a fixer upper. And I am learning a lot. I did notice that when I have the front panel is off it starts a little better. I read somewhere that if it were the sail switch to gently bang on the top when the fan kicks in. I will certainly look for the flashing LED.
Bear816 is offline   Reply With Quote
Old 01-15-2021, 01:59 PM   #6
Senior Member
 
Join Date: Jan 2018
Location: Raleigh, NC
Posts: 3,736
Aha!

Quote:
Originally Posted by Bear816 View Post
Unfortunately I do not have a history for anything on the motorhome. I just purchased a few months ago knowing it was a fixer upper. And I am learning a lot. I did notice that when I have the front panel is off it starts a little better. I read somewhere that if it were the sail switch to gently bang on the top when the fan kicks in. I will certainly look for the flashing LED.
When our regulator (on the small SOB trailer) was failing, it would operate perfectly--if the front panel was off. It turns out that with the front panel was off there is less resistance to the blowers. (In a Suburban furnace, there is one double-ended motor--shafts out both ends. There's a squirrel cage blower on each end. One circulates air inside the RV. The other draws outside air into the firebox and exhausts combustion products to the outside.)

It could be, as Mike suggests, that there's enough dust and pet hair inside that the blowers cannot operate fast enough to set the (safety) sail switch. There was enough dog hair in ours to make another dog.

It could also be (as was the case with ours) that the propane regulator is failing. The Suburban furnaces are very fussy about pressure. If it isn't exactly right (11" w.c.), it won't ignite.
__________________
Larry

Sticks and Bricks: Raleigh, NC
2008 Cherokee 38P: at Ivor, VA permanently
Larry-NC is online now   Reply With Quote
Old 01-15-2021, 03:59 PM   #7
Junior Member
 
Join Date: Jul 2020
Posts: 14
Quote:
Originally Posted by Bear816 View Post
I have been fighting with this furnace for days. It will start and will burn for one cycle. It shuts down but the next time it starts it is just the blower motor.....no flame. I checked the electrode assembly and it seems to be fine. I did notice that when it does start, the electrode sparks and when the burner runs, the electrode gets red hot. Is this the electrode still trying to run?

Similar problem with another older Suburban furnace in a '94 trailer getting little use, except mine will scream like a banshee (my neighbors should have called the sheriff) until I beat on the furnace box with a garlic press, the nearest tool at hand. That seems to release some part that gets hung up...perhaps the sail switch? When I start the furnace regularly/weekly, it always cooperates without complaint.
ElyWhy is offline   Reply With Quote
Old 01-15-2021, 04:15 PM   #8
Senior Member
 
Join Date: Jan 2018
Location: Raleigh, NC
Posts: 3,736
Two possibilities

Quote:
Originally Posted by ElyWhy View Post
Similar problem with another older Suburban furnace in a '94 trailer getting little use, except mine will scream like a banshee (my neighbors should have called the sheriff) until I beat on the furnace box with a garlic press, the nearest tool at hand. That seems to release some part that gets hung up...perhaps the sail switch? When I start the furnace regularly/weekly, it always cooperates without complaint.
There are only two moving parts in a Suburban furnace:
  1. The blower motor which is double-ended and has a squirrel-cage blower on each end.
  2. The gas solenoid which turns the gas on and off in response to commands from the control board. It makes a single "clunk" each time heat starts or stops.
So the noise is clearly coming from the blower assembly. Once again, there are two possibilities:
  1. One of the squirrel-cages is loose on the shaft and is either slipping or has slid along the shaft and one side is scraping on the housing. This should be easy to find and fix. You can clean out a lot of dust, pet hair, and gunk while you're in there. A toothbrush is helpful.
  2. The motor shaft bearings are dry. I think these bearings are porous bronze bearings. When they are manufactured, they are heated and dipped in oil. As they cool, oil enters the pores. Eventually all the oil is dispersed and the bearings run dry. Suburban states that the motor is permanently lubricated and should not be oiled.

Good luck and let us know how it comes out.
__________________
Larry

Sticks and Bricks: Raleigh, NC
2008 Cherokee 38P: at Ivor, VA permanently
Larry-NC is online now   Reply With Quote
Old 01-16-2021, 06:04 AM   #9
Member
 
Join Date: Dec 2019
Location: Lewis Center, Ohio
Posts: 81
Just a simple thought

If you have 2 propane tanks, make sure that it is switched to the one that has propane in it. As we all know, sometimes its a simple mistake that drives us crazy.
TGO Bill is offline   Reply With Quote
Old 01-16-2021, 08:00 AM   #10
Senior Member
 
nomad297's Avatar
 
Join Date: Jul 2015
Posts: 5,909
Quote:
Originally Posted by Larry-NC View Post
There are only two moving parts in a Suburban furnace.
Just messing with you, Larry, but technically, there are many more moving parts. Consider how many moving parts are in just one bearing and how many vanes are on a squirrel cage and all of the moving parts that make up the motor — the list goes on and on — there are hundreds of moving parts when you think about it this way, and just one of those parts could be causing the problem.

But, when considering how many moving parts there are that are actually replaceable, just like you stated; there’s not too many.



Bruce
__________________
2016 Rockwood Windjammer 3029W Diamond
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW
nomad297 is online now   Reply With Quote
Old 01-24-2021, 11:40 AM   #11
Senior Member
 
Join Date: Oct 2015
Posts: 484
Sail switch moves to. Open/ close.
__________________
Dale & Karen
2015 Lacrosse 311RLS
2006 F-250 The 06-6.0
Dwilcox is offline   Reply With Quote
Old 01-24-2021, 11:55 AM   #12
Senior Member
 
Join Date: Jul 2017
Posts: 2,505
Quote:
Originally Posted by Bear816 View Post
I have been fighting with this furnace for days. It will start and will burn for one cycle. It shuts down but the next time it starts it is just the blower motor.....no flame. I checked the electrode assembly and it seems to be fine. I did notice that when it does start, the electrode sparks and when the burner runs, the electrode gets red hot. Is this the electrode still trying to run?
Chances are it's sail switch since it's intermittent . the igniter also acts as a flame sensor and sends signal to the board telling it there is flame . it will get red hot since it sits in the flame . the igniter is spark not hot surface type . sail switches can be intermittent . i've seen them covered in dog hair which can make them not work , or they will work one time and not another because the internals will not make contact all the time .
MR.M is offline   Reply With Quote
Old 01-25-2021, 02:03 AM   #13
Just as confused as you
 
Scrapper's Avatar
 
Join Date: Aug 2013
Location: south central Wisconsin
Posts: 4,755
There is a Service Manual in the Library section of the forum which covers this NT-30SP and every other furnace Suburban makes. Suburban does not have a diagnostics LED on the control board mentioned by nather.

I may be wrong but I believe the NT-30SP has time delay fan control. Suburban made 12vdc and 24vac controls, the 24vac control needs a minimum of 18vdc which is supplied from 120vac step-down transformer. You need to verify the board number, the 12vdc Fan Control Module Board is Part Number 520820, the 24vac Fan Control Module Board is Part Number 520947.

I have attached a pdf for the Suburban Service Manual for your convenience. Sequence of operation description and troubleshooting starts on page 23.
Attached Files
File Type: pdf Suburban Furnace Service Manual.pdf (4.92 MB, 5 views)
__________________
Richard & Jill
2014 Flagstaff 832IKBS Classic Super Lite
2018 Silverado 1500 Crew Cab Z71 4WD All Star Edition
Camping since 1989
Car Shredder Op/Tech, Scrap Metal Recycling - retired
I deserve hazard pay when camping with my relatives.
Scrapper is offline   Reply With Quote
Old 01-25-2021, 08:43 AM   #14
Senior Member
 
Join Date: Jul 2017
Posts: 2,505
Quote:
Originally Posted by Scrapper View Post
There is a Service Manual in the Library section of the forum which covers this NT-30SP and every other furnace Suburban makes. Suburban does not have a diagnostics LED on the control board mentioned by nather.

I may be wrong but I believe the NT-30SP has time delay fan control. Suburban made 12vdc and 24vac controls, the 24vac control needs a minimum of 18vdc which is supplied from 120vac step-down transformer. You need to verify the board number, the 12vdc Fan Control Module Board is Part Number 520820, the 24vac Fan Control Module Board is Part Number 520947.

I have attached a pdf for the Suburban Service Manual for your convenience. Sequence of operation description and troubleshooting starts on page 23.
The furnaces in the RV are all 12 volt ! attwood and surburban do make them for small cabins and will be 120v with transformers but not the ones you find in RV's
MR.M is offline   Reply With Quote
Old 01-25-2021, 02:08 PM   #15
Just as confused as you
 
Scrapper's Avatar
 
Join Date: Aug 2013
Location: south central Wisconsin
Posts: 4,755
Here is a service manual specific to the NT-xxxx Series furnaces. As I suspected the fan has a time delay relay which works in conjunction with the control board.

It may be the time delay relay is experiencing failure when it gets hot.


You can download other documents for this furnace from https://pdxrvwholesale.com/products/...sp-tune-up-kit
Attached Files
File Type: pdf Suburban-Dynatrail-Furnace-NT_Series-Service-Manual.pdf (277.3 KB, 7 views)
__________________
Richard & Jill
2014 Flagstaff 832IKBS Classic Super Lite
2018 Silverado 1500 Crew Cab Z71 4WD All Star Edition
Camping since 1989
Car Shredder Op/Tech, Scrap Metal Recycling - retired
I deserve hazard pay when camping with my relatives.
Scrapper is offline   Reply With Quote
Old 01-25-2021, 02:54 PM   #16
Senior Member
 
Join Date: Jul 2017
Posts: 2,505
Quote:
Originally Posted by Scrapper View Post
Here is a service manual specific to the NT-xxxx Series furnaces. As I suspected the fan has a time delay relay which works in conjunction with the control board.

It may be the time delay relay is experiencing failure when it gets hot.


You can download other documents for this furnace from https://pdxrvwholesale.com/products/...sp-tune-up-kit
all time delay is built into the control board there is no separate relay . the firing sequence is call for heat , blower comes on , sail switch makes contact , then igniter and gas valve turn on , flame is sensed telling control board to continue operation , then heat satisfied t-stat breaks contact blower keeps running for cool down ! all this is controlled by the board , sail switch , igniter .
MR.M is offline   Reply With Quote
Old 01-25-2021, 03:33 PM   #17
Just as confused as you
 
Scrapper's Avatar
 
Join Date: Aug 2013
Location: south central Wisconsin
Posts: 4,755
Quote:
Originally Posted by MR.M View Post
all time delay is built into the control board there is no separate relay . the firing sequence is call for heat , blower comes on , sail switch makes contact , then igniter and gas valve turn on , flame is sensed telling control board to continue operation , then heat satisfied t-stat breaks contact blower keeps running for cool down ! all this is controlled by the board , sail switch , igniter .
Not according to the service manual (see Figure 6, top left), the parts list on the site in my post also lists a replacement number for the time delay relay (bottom, page 10).
__________________
Richard & Jill
2014 Flagstaff 832IKBS Classic Super Lite
2018 Silverado 1500 Crew Cab Z71 4WD All Star Edition
Camping since 1989
Car Shredder Op/Tech, Scrap Metal Recycling - retired
I deserve hazard pay when camping with my relatives.
Scrapper is offline   Reply With Quote
Old 01-25-2021, 05:09 PM   #18
Senior Member
 
Join Date: Jul 2017
Posts: 2,505
Quote:
Originally Posted by Scrapper View Post
Not according to the service manual (see Figure 6, top left), the parts list on the site in my post also lists a replacement number for the time delay relay (bottom, page 10).
not on the RV units . 12 volt all is incorporated into the board , no separate time delay switch unless you're dealing with a 30 yr old unit .
MR.M is offline   Reply With Quote
Old 01-25-2021, 05:11 PM   #19
Senior Member
 
Join Date: Jul 2017
Posts: 2,505
Quote:
Originally Posted by Scrapper View Post
Not according to the service manual (see Figure 6, top left), the parts list on the site in my post also lists a replacement number for the time delay relay (bottom, page 10).
SEQUENCE OF NORMAL OPERATIONThe electronic ignition system is made up of three main parts: the module board, theelectrode assembly, and the electrode wire. The module board is the brain of the electronicignition system and it has several functions.1.When the blower reaches approximately 75% of the normal rpm and sufficient airflow isestablished, the sail switch engages and completes a 12-volt circuit through the limitswitch to the module board. (NOTE: Low voltage power supply will not providesufficient motor rpm to
MR.M is offline   Reply With Quote
Old 01-25-2021, 05:12 PM   #20
Senior Member
 
Join Date: Jul 2017
Posts: 2,505
Quote:
Originally Posted by Scrapper View Post
Not according to the service manual (see Figure 6, top left), the parts list on the site in my post also lists a replacement number for the time delay relay (bottom, page 10).
After a 12-18 second delay, 12-volt current will pass through the module board to thesolenoid valve. The current to the valve opens it and allows gas to the main burner,simultaneously, the module board sends high voltage through the electrode wire to theelectrode assembly. The voltage seeks a ground between electrode and ground probeand a spark occurs. The spark.



The time delay is built into the control board.......
MR.M is offline   Reply With Quote
Reply

Tags
furnace, suburban

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Forest River, Inc. or any of its affiliates. This is an independent, unofficial site.



All times are GMT -5. The time now is 05:28 PM.