RV Repair: Suburban Furance, suburban furnace, furance

Question
I have a 2000 Winnebago with a Suburban Furnace model SF42 SN:000207002D  with a Coleman Mach thermostat.
at night we set the thromsat on 68  and the furnace will run all night, it won't shut down, after it gets up to 80  I get up and turn it completely off.  sometimes I notice the display on the thermostat is off
any Idea's?
Thanks for your help
Herb

Answer
Herb, It sounds to me like the trouble is in the T-Stat. This is probably a furnace that has a fan control board and they have been known to do some strange things, but in order to come on power has to get from one side of the T-Stat wires to the other. Also the T-Stat is there to regulate the temp by making and breaking this connection allowing the furnace to cycle on and off. I might try buying a inexpensive T-Stat (Heat only) and pulling off the wires to the furnace and hooking them to this one to see what happens then. If this seems to cure it then you might think about getting a new T-Stat that has both heat and cool controls. The reason I tell you to get the heat only is because the T-Stat your unit is using is pretty costly and if it is not the trouble then you spent around 100.00 for nothing. I hope this helps, Bill