Anyone else upgrade their thermostat and change the burn cycle of their furnace?

[4llamas]

With the original thermostat (non-digital, year 2009) my Atwood 8012 furnace would not shut off - a recent development. The gas would cut out but before the fan finished it's cool down cycle the furnace would reignite and continue in that off/on cycle until I manually turned off the thermostat. Or I could turn it way down and it would go off. This led to a couple of very uncomfortable nights at a trailhead camp, but fortunately it caused me to be awake at 3:00 am to hear the bear circling my camp. I think it was a little upset about my llamas. Anyway...

Back home a local technician did a bench test of the furnace control board and said it was good, my problem was the thermostat. That was good news; just the incentive I needed to upgrade to the digital Honeywell TH1100 heat only. So I did and it changed the way my furnace operates, but not so much for the better.

Now the furnace shuts off when it eventually gets to the set point, but on it's way to reaching set point the flame kicks in and out about every 12-15 seconds. The furnace grill never gets hot to the touch, just warm. I've only used the furnace a couple of times with the new thermostat and both times were at home, with the top down, in mild weather. Camper temp. was about 45 degrees and I set the thermostat to 60. After initially burning for about a minute the furnace began to short cycle and I doubt it would make the set point in colder weather with the top up.

Anybody else have issues like this?

Thanks

 

[rando]

I have the same Honeywell thermostat and have not seen this issue. As this issue seems to have effected two different thermostats, I can see two possibilities - that your thermostat is mounted too close to the heater output, causing it to short cycle or that there is something wrong with heater control board.

 

[Bigskyxj]

I went with a digital thermostat in my old hardside camper, heat only. It seemed to work great. The only problem I had was that the thermostat didn't work below 32 degrees unless I jumped the two wires.

A couple basic things I would check are:

Do you have propane?

Is your propane regulator starting to crap out? This is a possibility, usually when they crap out the flow of gas is intermittent or non existent. Check the flame color on the stove. If it has quite a bit of orange I would say you have a bit of a gas flow driven all over.

Your regulator should be set to 11 W.C. inches of pressure. There are quite a few good YouTube videos that show a home built manometer used to check this.

Is there a blockage in the propane line leading to your furnace?

Is there any blockages in your heater exhaust like mud swallows or hornet nests?

I would start with checking these items as a basic troubleshooting routine first.

 

[CougarCouple]

Hi 4llamas
You could use a multimeter to check if the stat is what is cycling off power to the furnace.
My thoughts are the unit is not proving flame and shutting off. With the stat still calling the unit tries and lights again.
That’s why it never gets warm, and takes extended time to heat your camper.
Russ

 

[lactic]

Very helpful thread. I have the original analog thermostat in my 2017 Fleet and have experienced the constant fan on cold nights. I didn’t realize it was the cool down phase running into another heating cycle. Makes sense.

Any other replacement thermostats people would recommend if the TH1100 is not ideal for the original poster’s application?

 

[Bigskyxj]

Another thing to consider is that most thermostats have an adjustable cycle time. I don't remember what I set mine to but the directions for the thermostat gave a recommendation and that's what I used.

 

[4llamas]

Thanks all. The stat is right where FWC left it. I do have a 3/4 tank of propane and both burners of the stove put put large clean blue flames, at the same time. It is curious to me that the issues of my furnace would change with thermostats. Perhaps one thing led to another. I suspect a problem within the furnace and have begun to read various troubleshooting articles including one describing the components and their functions. Not my favorite kind of who-done-it. Misery loves company so I thought I'd check in and commiserate figuring I can't be the first to have these issues. Thanks some more.

 

[4llamas]

Another thing to consider is that most thermostats have an adjustable cycle time. I don't remember what I set mine to but the directions for the thermostat gave a recommendation and that's what I used.

I didn't realize the Honeywell TH1100 had that adjustment. I will look into it. Is this the same thermostat you have?

 

[Bigskyxj]

I didn't realize the Honeywell TH1100 had that adjustment. I will look into it. Is this the same thermostat you have?

I'm fairly certain that it is.

 

[4llamas]

Another thing to consider is that most thermostats have an adjustable cycle time. I don't remember what I set mine to but the directions for the thermostat gave a recommendation and that's what I used.

Is this what you are referring to: Page 7 of the Installation Guide: Setup Function #5 Heating Cycle Rate, default is for oil or gas furnaces < 90% efficient.
Sounds about right, but I suppose I could try others. I will look and see how it is actually set. Thanks

 

[rando]

Thanks all. The stat is right where FWC left it. I do have a 3/4 tank of propane and both burners of the stove put put large clean blue flames, at the same time. It is curious to me that the issues of my furnace would change with thermostats. Perhaps one thing led to another. I suspect a problem within the furnace and have begun to read various troubleshooting articles including one describing the components and their functions. Not my favorite kind of who-done-it. Misery loves company so I thought I'd check in and commiserate figuring I can't be the first to have these issues. Thanks some more.

The minimum cycle time between the mechanical and digital thermostats is different, which would explain why the issue is different between the two thermostats.

One way to check if it is the thermostat or furnace would be to jumper the two wires that go to the thermostat together - the furnace should run continuously. If it still cycles on and off, the issue is with the furnace.

 

[4llamas]

The minimum cycle time between the mechanical and digital thermostats is different, which would explain why the issue is different between the two thermostats.

One way to check if it is the thermostat or furnace would be to jumper the two wires that go to the thermostat together - the furnace should run continuously. If it still cycles on and off, the issue is with the furnace.

Before I break out the multi-meter I'll bypass the thermostat and see how the furnace cycles, and I will also see how the thermostat is set to cycle. The furnace seems more suspect to me than the thermostat, but I am out of my strong suit here. I will report back, probably in a few days after I finish smearing paint on bedroom walls and complete a few chores.