Furnace - thermostat extremes

[Sans1]

Took the RV out the week prior to/through memorial weekend and temp ranged from 30 degrees at night through 80 (inside). Before I begin, issue was same whether on DC or Gen Power. When thermostat was showing below 60 degrees, enough to need the heat, set the temp to 65, furnace did not want to come on (waited for several minutes before turning it up) unless cranked into the 70's. Then after finally coming on, would adjust thermostat to 65,but furnace would run so long it would get too warm before finally, without touching it, it would shut off (thermostat would show 70 something). Eventually it would get way too cold before the heat would come back on (less than 60 - even though it was set to 65. It SEEMED to take a 10 degree change before the heat would come on/shut off. Is this normal? I have hard time believing that it is My first thought is to replace the thermostat.

I am not home now but I believe it is a Dometic thermostat.

 

[danemayer]

Hi Sans1,

Did you cycle the thermostat to see what it was reading as the ambient temperature? One possibility is that something is confusing the thermostat. For example, if you have a heater running in the basement, the hot air will rise behind the wall where the thermostat is mounted.

 

[Sans1]

there were no other sources of heat. I was just looking at the thermostat, seems if it says 70, and it was set to 65, heat would be off. It does appear that the 'return air' is right below the thermostat ~ 5 feet below it. But again, referencing the display, seems it should not matter. I wll geta external sensor to compare when get a chance

 

[danemayer]

We have a Dometic Single Zone LCD and the display shows the set point, not the ambient temperature. I have to cycle the thermostat to OFF and then press the + or - button to display ambient temp.

The manual for the Dometic Comfort Control II thermostat says you have to press and hold the INSIDE TEMP button to get the ambient reading. The normal display at rest is the set point.

 

[Sans1]

We have a Dometic Single Zone LCD and the display shows the set point, not the ambient temperature. I have to cycle the thermostat to OFF and then press the + or - button to display ambient temp....

Thanks, I'll need to confirm what I actually have.
I don't think mine has that feature, unless there is a combo of buttons that need to be pressed. I think I have "mode", "+" and "-" , I'll check when I get home. I'm so confused on what I thought I observed, at this point I can't remember if the 'untouched' thermostat number was going up with the temp, or that was the number we kept raising trying to get it to come on when too cold inside. Either way we are doing something wrong, or it is not working as expected. In the hands off method I have to put in my hoodie until it finally comes on and runs for a while, then before it shuts off I am shedding it again..