Suburban SF30 high temp

[Hewster]

My trailer has the “winter” package or whatever you would like to call it so has the 30k btu furnace instead of 20. With a single little 2” duct running into underbelly.

I’ve found a few other posts of people having issues with it going down on high temp (fan stays running, when cools down furnace will ignite again and run till set point is made or over temp)

No vents covered, blocked or shut off.
Thinking of adding another 2” duct to vent out some of the heat as well? Anyone else have resolution with an issue such as this?

 

[Isaac-1]

If you have not done so yet, you may want to replace the high temperature limit switch as they can get weak as they age and trip at lower temperatures.

 

[Hewster]

If you have not done so yet, you may want to replace the high temperature limit switch as they can get weak as they age and trip at lower temperatures.

Have not done so yet. (Trailers only 3 years old now)

But was planning to change it out in spring when my trailer comes out of storage anyways. Cheap and relatively easy.

 

[Kirk]

Are you saying that your furnace only has 1 outlet heat duct of 2" diameter, or that the one into the belly is 2" but there are others? The most common cause for a furnace cycling on the high limit thermostat is crushed or blocked ducts but I have never seen one that had only 1 vent so if that is the case, it may well the problem. It is quite common for an RV furnace to have unused heat discharge blanks so you should be able to add another duct, if none are blocked in any manner. Has your furnace worked properly at one time and this just started, or is it new?

 

[Hewster]

Are you saying that your furnace only has 1 outlet heat duct of 2" diameter, or that the one into the belly is 2" but there are others? The most common cause for a furnace cycling on the high limit thermostat is crushed or blocked ducts but I have never seen one that had only 1 vent so if that is the case, it may well the problem. It is quite common for an RV furnace to have unused heat discharge blanks so you should be able to add another duct, if none are blocked in any manner. Has your furnace worked properly at one time and this just started, or is it new?

No sorry,

I have multiple ducts and my main is a down draft through the floor

I meant that 2” is the additional “heated underbelly” vent. There is more cutouts available to add ducting

 

[Kirk]

If the furnace worked properly for 3 years but is now operating on the high limit thermostat, something must have changed. It is possible that the change was the high limit thermostat has failed. You need to get one specific to the model of furnace that you have as they do not all have the same temperature set point. If you have access to a way to measure the temperature of that heat exchanger when the thermostat opens, that would be very helpful.

 

[Gary RV_Wizard]

A failed high limit sensor is conceivable, but the more likely fault possibilities are:

• Dust bunnies in the ducting
• A crushed or kinked duct
• Closed outlet vents (physically check them all, carefully)
• Dirty or blocked circulation air intake at the furnace

 

[Hewster]

Are you saying that your furnace only has 1 outlet heat duct of 2" diameter, or that the one into the belly is 2" but there are others? The most common cause for a furnace cycling on the high limit thermostat is crushed or blocked ducts but I have never seen one that had only 1 vent so if that is the case, it may well the problem. It is quite common for an RV furnace to have unused heat discharge blanks so you should be able to add another duct, if none are blocked in any manner. Has your furnace worked properly at one time and this just started, or is it new?

One 2” into the belly along with the ducting running through to the other 3 vents.

 

[Kirk]

One 2” into the belly along with the ducting running through to the other 3 vents.

That is pretty typical. So have you found anything? Did you check all of the ducts?

 

[Hewster]

That is pretty typical. So have you found anything? Did you check all of the ducts?

Yea it’s the norm I’ve found. The 3 other vents have great flow through them.

Not a it ran great for 3 years situation. It’s done it for a couple for sure. Didn’t use it towards winter much the first year.
- also had another propane issue with it the first year that the fitting on the heater side of gas valve was loose and would get a hint if propane only when heater running. Finally got fed up waiting pulled it myself and found that.

- that’s why I’m leaning towards adding another 2” vent off the furnace. I’ve done some reading and have found people say they upgraded from a 20k to 30k btu furnace for the “arctic” or whichever winter package you went to call it. But nothing else changed ducting wise so a common issue