Heater won't go above 67 deg.

[Mammoth]

I have a quick question. We have a suburban heater in our trailer and for some reason no matter what I set the thermostat at, it will never get above 67 deg in the camper. The heater shuts off even thought the thermostat isn't at the set temp. Anyone have any ideas why this might be happening? Any help would be appreciated. I have a wolf pup 16bhs if that matters.

[ependydad]

Sorry this thread runs afoul of the new “sunshine and rainbow” rule.

Forest River Issues Cease and Desist to FRF - they’re trying to shut us down!

[Mammoth]

Originally Posted by ependydad

Sorry this thread runs afoul of the new “sunshine and rainbow” rule.

Forest River Issues Cease and Desist to FRF - they’re trying to shut us down!

Sorry I didn't realize. I was just looking good help. I apologize

[ependydad]

Originally Posted by Mammoth

Sorry I didn't realize. I was just looking good help. I apologize

Naw, I’m an idiot and it’s April 1st and all.

[Mammoth]

Originally Posted by ependydad

Naw, I’m an idiot and it’s April 1st and all.

Lol I'm a fool. You got me.

[5picker]

Is the 'stat positioned near a register? Often times that will make it shut off too soon.

Also pull the 'stat and check how big the hole is where the wiring comes through behind it. Often times if the 'stat is mounted on a wall where heat can build up (like on a wall housing the refrigerator) the heat can escape into the back of the 'stat and turn it off prematurely.

[Larry-NC]

Originally Posted by 5picker

Is the 'stat positioned near a register? Often times that will make it shut off too soon.

Also pull the 'stat and check how big the hole is where the wiring comes through behind it. Often times if the 'stat is mounted on a wall where heat can build up (like on a wall housing the refrigerator) the heat can escape into the back of the 'stat and turn it off prematurely.

Well, yes, but that wouldn't make the furnace totally insensitive to the thermostat setting--just the numbers would be off. For example, if you set 72 and it kicked off at 67, then if you set 82 it would kick off at 77 or so.

The Suburban furnaces have an over-temperature sensor. If the outlets are restricted (floor vents covered with mats, for example, or dust in ducts), the heat exchanger will get too hot and the sensor will open. It's like a fixed temperature thermostat in series with the adjustable one on the wall. When it cools down, it will reset.

If you take the grille off the furnace and then take the front facing cover off the furnace heat exchanger, the over-temperature sensor is sitting right in front of you in the center, about 3/8" wide, 1-1/2" long, with a wire connected at each end.

When the furnace is running, there should be 0 volts across it. If it trips, there will be 12v as it is opening the circuit. If this were me, I'd clip fine wires on each end, put the cover back on, and monitor the voltage to see whether this overtemp sensor is tripping. Someone else probably has an easier way.

Larry

[Mammoth]

Originally Posted by Larry-NC

Well, yes, but that wouldn't make the furnace totally insensitive to the thermostat setting--just the numbers would be off. For example, if you set 72 and it kicked off at 67, then if you set 82 it would kick off at 77 or so.

The Suburban furnaces have an over-temperature sensor. If the outlets are restricted (floor vents covered with mats, for example, or dust in ducts), the heat exchanger will get too hot and the sensor will open. It's like a fixed temperature thermostat in series with the adjustable one on the wall. When it cools down, it will reset.

If you take the grille off the furnace and then take the front facing cover off the furnace heat exchanger, the over-temperature sensor is sitting right in front of you in the center, about 3/8" wide, 1-1/2" long, with a wire connected at each end.

When the furnace is running, there should be 0 volts across it. If it trips, there will be 12v as it is opening the circuit. If this were me, I'd clip fine wires on each end, put the cover back on, and monitor the voltage to see whether this overtemp sensor is tripping. Someone else probably has an easier way.

Larry

Thanks I figured it was some kind of safety shut off. Just odd I can't get it to go above 67. I'll have to do some more research.

[Mammoth]

Ok so after messing with it some. I noticed that the heater now won't stay on. When the thermostat calls for heat the blower turns on, and the long bar inside ignites. But after about 10 seconds it goes off. It does this 3 times then shuts down till I turn the stat off and on again. And from what I can see with a flashlight it looks like the fan way in the back isn't spinning super fast. I'm camping this week so not having heat the next few nights is going to be rough. Anyone have any ideas or anything I can try in the field? The camper is only 2 years old and the furnace is a suburban nt-20seq. Any help would be greatly appreciated.

[Larry-NC]

Originally Posted by Mammoth

Ok so after messing with it some. I noticed that the heater now won't stay on. When the thermostat calls for heat the blower turns on, and the long bar inside ignites. But after about 10 seconds it goes off. It does this 3 times then shuts down till I turn the stat off and on again. And from what I can see with a flashlight it looks like the fan way in the back isn't spinning super fast. I'm camping this week so not having heat the next few nights is going to be rough. Anyone have any ideas or anything I can try in the field? The camper is only 2 years old and the furnace is a suburban nt-20seq. Any help would be greatly appreciated.

The Suburban lighting sequence goes like this:

• Run the fan for about 7 seconds to exhaust any propane from previous attempts. (Because the combustion fan and duct fans are coupled to the same motor, the duct fan will run too.)
• Check "sail switch" to make sure that fan is running fast enough to proceed
• Open the propane valve and attempt to light.
• If the heat sensor (thermocouple) senses that that the burner has lit, all is good. Else exhaust for a few seconds and try again.
• Make three attempts. Then go into "lockout." The furnace will not retry until the thermostat is turned on and off (either turn from Heat to Off or turn temp lower than current temp and back).

Therefore, if you actually see the flame ignite (or hear it go "whump"), you are making it through the first three steps and failing the fourth (thermocouple) step.

If you are up for this kind of repair, enter
suburban rv furnace thermocouple into Google and you will see directions and YouTube videos on what to check. It could be that the thermocouple isn't positioned in the flame, or not firmly connected to the controller board. Or it could be a defective thermocouple or controller board. The first two are much more likely.

This job requires some skill. If you're not confident, get service.

Larry

[Mammoth]

Originally Posted by Larry-NC

The Suburban lighting sequence goes like this:

• Run the fan for about 7 seconds to exhaust any propane from previous attempts. (Because the combustion fan and duct fans are coupled to the same motor, the duct fan will run too.)
• Check "sail switch" to make sure that fan is running fast enough to proceed
• Open the propane valve and attempt to light.
• If the heat sensor (thermocouple) senses that that the burner has lit, all is good. Else exhaust for a few seconds and try again.
• Make three attempts. Then go into "lockout." The furnace will not retry until the thermostat is turned on and off (either turn from Heat to Off or turn temp lower than current temp and back).

Therefore, if you actually see the flame ignite (or hear it go "whump"), you are making it through the first three steps and failing the fourth (thermocouple) step.

If you are up for this kind of repair, enter
suburban rv furnace thermocouple into Google and you will see directions and YouTube videos on what to check. It could be that the thermocouple isn't positioned in the flame, or not firmly connected to the controller board. Or it could be a defective thermocouple or controller board. The first two are much more likely.

This job requires some skill. If you're not confident, get service.

Larry

Thanks. I'm not sure I'm comfortable messing with it. Guess I'll just bring it in for service. Thanks

[D. J. Schuler]

You might want to check propane supply and possible regulator freeze-up. If you are in NJ we,ve had some pretty cold weather.

[Spikedog]

Larry-NC has some good advice there. DJ too (there is fuel in the device, no?).

If you were only making it to step 2 (sail switch), you might be able to fix it with a good thwack with a hammer in the right spot. Sadly, your problem sounds more complicated. Good luck.

[5picker]

Larry's diagnostic steps are spot on.

In 40 years, I've had two furnaces that got to the same step as yours... lights but shuts off in about 10 seconds, tries three times and goes into lockout. Both times it was the control board.

If you do replace the board, Dinosaur Electronics makes a replacement board that is head and shoulders above the factory board.

Dinosaur Electronics.

[Mammoth]

Originally Posted by D. J. Schuler

You might want to check propane supply and possible regulator freeze-up. If you are in NJ we,ve had some pretty cold weather.

We're in Maryland and it's been in the high 30s at night so it's possible

[Mammoth]

Originally Posted by 5picker

Larry's diagnostic steps are spot on.

In 40 years, I've had two furnaces that got to the same step as yours... lights but shuts off in about 10 seconds, tries three times and goes into lockout. Both times it was the control board.

If you do replace the board, Dinosaur Electronics makes a replacement board that is head and shoulders above the factory board.

Dinosaur Electronics.

Thanks I'll look into it.

[johng4706]

While I have nothing to add to the above, I'd like to offer a suggestion.

Get an electric space heater, particularly if you are in a campground with power. Saves on LP gas and much quieter.

[Mammoth]

Originally Posted by johng4706

While I have nothing to add to the above, I'd like to offer a suggestion.

Get an electric space heater, particularly if you are in a campground with power. Saves on LP gas and much quieter.

I actually ran to Walmart last night and got a small tabletop ceramic heater with a fan. Kept the camper at a comfortable 72 all night. So I'll use that until I can get a service appointment.