Furnace Cycles

[chinook507]

Have a 2013 Cougar 32RBK Xlite and the furnace burner cycles on and off while the blower continues to run until the set thermostat temperature is reached. Was wondering if this is normal?

[joebedford]

The Atwood manual says: fix the ducting, replace the limit switch, adjust LP pressure.

[dougrainer]

Wild Bill 888 wrote:
“Normal. Ours does that so that it doesn't overheat when running for longer periods of time. Safety feature of the furnace.”

Circuit breakers are a safety feature, but if you are relying on a breaker to pop every five minutes you are relying on the last layer of protection, and are not safe. What happens when the contacts of the over temperature switch weld themselves together from excessive cycling?

I have never seen that(40years). What usually happens on a Hi Limit that has too much duty, is, it stays OPEN and the furnace will not heat. The Bi Metal inside finally gives up and the default is to NOT make a closed circuit. Doug

[Wild_Bill_888]

“Normal. Ours does that so that it doesn't overheat when running for longer periods of time. Safety feature of the furnace.”

Circuit breakers are a safety feature, but if you are relying on a breaker to pop every five minutes you are relying on the last layer of protection, and are not safe. What happens when the contacts of the over temperature switch weld themselves together from excessive cycling?

[Boon_Docker]

Yes, there is a safety feature called a high limit switch that shuts the burner down if the heat exchanger gets too hot. But cycling on and off continually is not a normal operation for the furnace.
There are a variety of reasons for cycling, but the two most common reasons are restricted ducts and faulty limit switch.

[doxiemom11]

Normal. Ours does that so that it doesn't overheat when running for longer periods of time. Safety feature of the furnace. Now I don't mean it goes on and off every 15 seconds, but runs for 4-5 minutes, then off, cools a couple minutes all the while the fan is blowing warm air yet, then burner re-lights and heats for a few more minutes etc.

[Wild_Bill_888]

If the air flow is vigorous and unobstructed, and the discharge temperature is high, consider lowering the gas pressure to reduce the heat rate to the point where the burner does not cycle.

Thermal cycling at high temperature accelerates heat exchanger aging and promotes cracking.

High altitude reduces heat transfer, increasing heat exchanger temperature, another reason to reduce heat rate.

[time2roll]

garym114 wrote:

chinook507 wrote:
Have a 2013 Cougar 32RBK Xlite and the furnace burner cycles on and off while the blower continues to run until the set thermostat temperature is reached. Was wondering if this is normal?

This is the way my Atwood heater has operated for the 13 years that I have owned it.

Mine also for a decade before I fixed it.

[garym114]

chinook507 wrote:
Have a 2013 Cougar 32RBK Xlite and the furnace burner cycles on and off while the blower continues to run until the set thermostat temperature is reached. Was wondering if this is normal?

This is the way my Atwood heater has operated for the 13 years that I have owned it.

[imgoin4it]

I always thought that not to be normal, but mine does the same.. Dealer tech says normal. Had a friend with different brand of coach. His did same. Not sure what is right but mine has been working that way for 11 years. I just don’t worry about it anymore.

[chinook507]

I scoped my floor ducts and did not see any blockages, furnace has 4 ducts, 1 in the forward area, 1 in the living area, 1 in the rear bunk area, and 1 in the bathroom. All ducts are wide open, nothing restricted from what I can see.

[time2roll]

Not normal. The existing ducts are either inadequate or blocked from debris or poor installation.

Mine was poorly installed to minimum spec with joints blocking air flow and floor insulation collapsing the duct. I ended up adding two additional ducts using the 4" knockouts. Tons of heat now and burner runs until the thermostat is happy.

[dougrainer]

Chris Bryant wrote:
No, it isn’t. Check the ducting for blockages or recirculating hot air. It is never good for it to cycle on the limit switch.

Also, you need the install specs for your model furnace. RV furnaces require the correct amount of duct tube knock out plates in use to prevent overheating. Your furnace is overheating and that is what is causing the burner to short cycle. There are 2 ways a furnace is ducted and BOTH may be utilized at the same time.
1. 4 inch round knock outs with 4 inch duct tubes
2. THRU the floor ducting which the output of the furnace on the BOTTOM is forcing air thru a in the floor duct system.
Last, it is not a good idea to cut off or restrict a duct to stop heated air from causing an area to get too hot. THAT will restrict and cause burner short cycling also. Doug

[Chris_Bryant]

No, it isn’t. Check the ducting for blockages or recirculating hot air. It is never good for it to cycle on the limit switch.

[JimK-NY]

yes