The furnace refuses to light intermittently

M-S

Member
I have taken my camper back to the dealer, under warranty, thankfully. Just wondering if others had the same problem and what was the solution if anyone has had this issue. Sorry this post is long, but you have to know what has happened to understand the concern.

History first, so you understand what has been done already. Last winter (2010) we had issues with the furnace not wanting to light when it was switched on at the thermostat. AC unit worked properly, no problems. Temperature was consistant on AC. Heat, not so good. When we would go to the camper at our RV campsite, on the weekend, and turn the furnace on, sometimes it would light correctly. It would turn on the blower, as it is supposed to, then try to light up to 3 attempts. Sometimes it would light right off, but sometimes it would go through all 3 and not light. Turn off the switch, wait a few minutes, and then turn it back on. You could smell gas outside, so I know the gas valve was and is still working to supply gas to the chamber. The dealer sent a repair guy to look at it, and they replaced the LP regulator, told us that it was bad. They even replaced the thermostat OK thought we were good to go, and went that next weekend and no joy. Same ole same o. End of season, it would work more often than not. Thought it was just the way it was designed, not at all happy.

Now. Went on a trip the last week, and had tried the heat, it worked fine, before we left, thought it would be fine. WRONG. On the 3rd night of the trip it was chilly, and tried the furnace, it did work and cycled like it should have done, thought things were great. 4th morning, it would not light and it got cold. Turned the switch off, and back on, things went to working. That evening, after traveling about 90 miles, getting to the weekend camping site, Temp in the low 40's outside, turned the furnace on, worked great that day, and into the night. However, on Saturday morning, it was back to its old tricks. Openned the outside cover, looking for any clue. Moved a couple of wires to see better, and turned the unit back on, worked. Didn't last. Had to move the same wires that went to the circuit board to the left of the motor, and then the unit worked. Called the dealer from the road, and told them I would be back in on Tuesday of this week, and was unhappy with the performance of this unit. Same problems all weekend, and Monday night on the way home we stopped, and it worked one cycle to heat the camper, and then would not light to produce heat. Thankfully I have a second unit with a heat pump, so I can heat the camper while on shore power. Had a generator over the weekend providing power, and didn't want to overload the generator.

Today, the dealer told me that they had worked on it, and it was not working. They took the unit out, and readjusted the fan blades to get more air to the cell inside the chamber, and they thought it was working. Put it back in, and no joy. They are working on it.

Has this happened to others, and what was the cure. I am told Suburban is a good heating unit. Water heater works fine. All the LP bottles are on, and at least one is full, and the other one is about half full, so that is not an issue. You can smell gas when it is trying to light so I am convinced that gas is not the issue. It is electrical, but what.

Thanks all for any help. I am asking in case the dealer runs into a brick wall. Obviously a new furnace is the last resort.
 

GOTTOYS

Well-known member
Like most everyone else here we can only offer precision guesswork as to what is wrong. In my opinion..there are people that work on RVs and there are people that work on furnaces...They are both real good at their job but maybe not so good at the others' job. Shouldn't be hard too find a certified furnace repair person and have them look at it. These are not rocket science and shouldn't be hard to fix, rather than shotgunning parts at it hoping to fix it...If they are a certified repair center they can do warranty work just the same as a dealer and will get a pre-authorization to work on it and can bill the manufacturer directly if it's under warranty...JMHO...Don
 

wdk450

Well-known member
Without having worked on a furnace at all I am just going to throw out my guesses based on what you have described. I think you have some sort of an intermittent electrical wiring problem. It may be the crimp connectors to the wires, it my be a corroded connection at a connector/circuit board, it may be a bad solder joint on the circuit board. The easiest thing to try is to spray all of the electrical contacting points you can with electrical contact spray. Radio Shack has the Cramolyn stuff I swear by. If you can, pull a bit on any crimped wire/connector conncection and see if it comes apart. Inspect the crimp if you can to see if the crimp is made over the wire insulation instead of stripped bare wire. If you can, solder as many of these crimped connections you can. Solder connects the two metals (wire and connector pin) on a molecular level eliminating the possibility of oxidation corrosion between the metal surfaces. The last and most expensive thing to try may be a new circuit board. Dinaosaur Electronics makes replacement boards said to be of better quality than the originals.
If there are loose connections, any movement of the wiring may fix/break the furnace temporarily, as the connections are made/broken by movement. Travelling down the road can likewise shake the connections. Even the expansion/contraction of metals due to temperature changes can be enough to break/make a poor connection.
Good luck!!!
 

slmayor

Founding California Northern Chapter Leader
Recently we've had to trouble shoot some furnace issues with different units at work that all relate back to the propane supply hoses. If you have the type with the big green knob on the end, try replacing it with a "wrench-on" type of hose. There seems to be a defect in seating the other type in the regulator that may trigger the excess flow prevention safety device. In other words, they aren't seating deep enough, and when a high demand appliance is on, they shut off. You can still smell gas, as some will flow before it shuts off.
Other things that happen are spider webs inside the units, bad motors (they will spin, but not fast enough to trigger the sail switch consistently) We have three brand new motors in boxes that were defective on install. The motors were bears to finally diagnose, as you have to leave the unit running on the bench until the motor heats up and test the output.

Just some more food for thought. On a positive note, if they're cleaned and maintained, they rarely fail. We work on 20 year old units every day.
 

M-S

Member
Thanks for the information. Dealer is not a certified repair center, but has a service guy there. They took the furnace out twice, and finally got information from Suburban, and the igniter stick in the furnace was supposed to be 1/16" inch from the burner, and ours was 3/16". So that was repaired, and they sent me on my way. Used the unit over the weekend, and it did not change anything. I guess shaking down the road may have undone what they worked on. Going to call Camping World and talk to their people. May get lucky and they can find the problem. Going to check the wires on the circuit board etc as has been suggested. Also the LP fittings on the tank are the green handle type. Will look into the idea of replacing them. My nickel if I have to.

Thanks all. I see that this is a common problem. Shouldn't be. But it is what it is.

Mark and Sue
 

larryanddonnakeever

Past Oklahoma Chapter Leaders (Founding)
I have been working on HVAC for 35 years, but I have only been RVing for 9 months. So here is what I would do to trouble shoot if it were mine. You need a volt/ohm meter and a gas pressure meter. be in the position to see the gas valve and the pilot / burner area. When the thermostat calls for heat the fan comes on and then the igniter lights the burner. If either of these fail you need to look at the igniter for a spark if you hear it clicking, the igniter should be close enough. If it is not close enough adjust the spark gap it should be 1/16" from the burner. If it is sparking and the burner does not light check voltage at gas valve terminals should be 12vdc. if you have voltage at gas valve and burner does not light check gas pressure at gas valve. There is a port on the outlet side of gas valve take the allen head screw out and screw in the fitting and connect rubber hose to fitting. These parts come with your pressure tester, you should have at least 3.5 inches of water column pressure for propane. If you have voltage at gas valve and no pressure out of the valve and you have gas pressure on the inlet side of gas valve then your gas valve is bad.. The intermitten problem could also be the control board in that case you won't have voltage at gas valve... Also double check all wire connections if necessary pull wire off terminals and lightly squeese the terminal end for a tighter fit. Good luck...
Larry Keever
Oklahoma City, OK.
 

savin

Member
My furnace has been messing up also. Here in Cleveland appliance repair can get a little costly. That's why I'd prefer to try on my own first. I will try some of what I read and let you know how it worked. Thank you, Dan.
 
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cookie

Administrator
Staff member
Dan, welcome to the forum. This is a great place to gather and share information. It looks like you have found that out already.
Let us know what you find out on your furnace.

Peace
Dave
 

mesteve

Well-known member
We had this same problem earlier this year. It was the thermocouple accessible from the grate side of the furnace. Jumpered past it and we had heat every time. Dealer said they could not duplicate but it definately was the fix while we were out...
 

jimtoo

Moderator
Hi 10377586,

Welcome to the Heartland Owners Forum. We have a great bunch of folks here with lots of informatin all willing to share their knowledge when needed.

If your having a problem with your furnace I suggest you contact a qualified repair person. To many things could happen that might not be good messing with propane and flames unless you know exactly what your doing.

Jim M
 

danemayer

Well-known member
If the furnace goes into "lockout" mode after it fails - meaning the blower continues to run, pushing cool air, and you have to cycle the thermostat to off and back to heat to try again - the gas failed to ignite. I've attached what Suburban says for servicers to check when this is the failure.

Suburban says to leave this to qualified servicers, but if you understand the possible causes, you can ask your servicer if he's checked these things:

Blower Runs but Burner Does Not Light:
1. Make sure the manual shut-off valve is in the "ON" position.
2. Possible air in the gas lines. Reset the thermostat and cycle the furnace several times
to bleed the system.
3. Check the gas supply. Be certain 11" WC pressure is present while the furnace is
operating.
If not, adjust the pressure regulator. (highlighting added - also my comment that it could be a hose problem)
4. Check the wiring for proper polarity.
5. Check for proper clearances down the sides and across the top for return air to feed
the room air blower. Each model furnace has a minimum requirement of return air
outlined in the installation manual. With improper return air, the air volume may not
actuate the sail switch that sends voltage to the module board. All models must have
I" clearance along the sides and across the top except the NT-34, -42 and -45 models,
which require 2" on the sides and top.
6. Check the ducting of the furnace to determine proper airflow away from the furnace.
See the installation manual for correct duct requirements. If the ducts have severe
bends or kinks in the hose, the airflow may be restricted enough to cause the
microswitch to bounce back from the volume of air hitting the cabinet front. This again
will not allow voltage to the module board. Many times, a furnace will operate
satisfactorily on the bench or without the cabi.net door on the unit. Check for
microswitch energizing when this happens. Correct ducting for proper airflow and/or
replace the microswitch (could be stiff).
7. If the furnace will ignite with the cabinet front off, but will not with the cabinet front
secured, and the ducting is free, check the gaskets around the burner access door. If
the burner access is not properly sealed, air may be deflected from the cabinet front
into the burner area, thus disturbing air and gas mixture for proper ignition.
8. Check for 12 volts DC on both sides of the limit switch. If there is voltage on one side of
the switch, but not on the other, replace the switch. If voltage is present on both sides
of the switch, proceed to Step 9.
9. Check for 12 volts DC at the power terminals on the module board (refer to the wiring
diagram - red wire positive and yellow wire negative). If no voltage, check wiring from
the limit switch. Correct wiring.
10. 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.
11. Make sure electrode is not grounding to burner, the gap between the spark probe and
the ground probe is 1/8" (see Figure 7), and the ceramic insulator is not cracked,
broken or sooted. Adjust, clean or replace as necessary.
12. If sparking is not audible, check the module board and observe if the neon bulb on the
circuit board is flashing during the trial for ignition. Remove the white plastic wire
connector from the circuit board. Clean the board terminals on back with a soft rubber
eraser. Check the little pin terminals in the plastic connector for good contact. Reinstall
connector. If the tube does not flash, replace the module board.
13. Check for voltage at the gas valve during the trial for ignition. If no voltage and
connections are okay, replace the board.
14. If the valve does not open with 12 volts DC present, replace the valve.
15. If the electrode sparks and the valve opens but the burner will not light, check the gas
supply for 11" WC pressure to the main burner office. If 11" is present to the valve but
not to the orifice, replace the valve. Check vent and air intake installation. Check the
main burner for correct relationship to the electrode assembly (burner should be 3/16"
from the spark probe and sawports or charge ports directly under the spark gap).
Check main burner for soot build-up in ports (see Figure 8). Clean cast-iron burners by
passing a hacksaw blade through the sawports, being careful not to enlarge the
openings. Wire brush stainless tube burners to remove build-up.
16. Check the combustion air wheel for proper rotation. Insufficient air will not sustain the
flame if the wheel is installed backward.
 
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