Have you experienced this annoyance?
It's a bit chilly in the camper, maybe 65 degrees. You nudge up the thermostat just a touch. The furnace comes on - and runs and runs and runs. As the inside temp rises past 80 with no sign of letup, you drop the thermostat back a bit until the furnace shuts off. And now the furnace doesn't come on again until the temp drops to 60.
This is really annoying. It is caused by the fact that, as the room heats up, the warmer air doesn't get inside the thermostat housing very well, so the thermostat doesn't realize the room has heated up, and it keeps calling for heat. There is a fix for this built into the thermostat, but it may need adjustment - mine did.
There is actually a tiny adjustable heater built into the thermostat. When the thermostat calls for heat, this tiny heater turns on and heats up the thermostat's sensor. If the heater is adjusted correctly, it heats the sensor at the same rate that the room warms up. At the same time that the room gets to the right temp, the sensor is warm enough and turns off the furnace.
To adjust the tiny heater, first pull the cover straight off the thermostat - it comes off easily. Everything inside is low voltage, so you can't get a shock, but work carefully since some of the components are delicate. The adjustment for the preheater is the small copper arm shown at the tip of the arrow in this
PHOTO. As you can see, the arm can swing from about the 7 o'clock position to the 10 o'clock position. In my TM, the arm was set at the fully down position (7 o'clock), which corresponds to no preheat. If the arm is fully up (10 o'clock), there is too much preheat - the furnace shuts off before the room warms up. The position shown in the photo is about 9 o'clock, but this was still too high in my rig. The correct position turned out to be about 7:30 - 8 o'clock.
You need to determine the right position by trial-and-error. It is time-consuming, but not hard. Replace the cover during each trial, of course.
Bill