I've read other posts on this useful forum and checked my unit as follows:
The filter is clean, the batteries in the thermostat are new, there are no loose wires. One thing I read and followed in another thread was to tap/jiggle the connector (I think it has 9 wires, including 2 yellow) at the bottom of the board. I did so and the unit begins working correctly and the house is nice and warm. However, this is not permanent and I have to jiggle to connector every few days. I'm trying to attach a picture of the connector, but don't see any "attach" button. Could there be something wrong with the connector or the wires leading to it? Or the board that the connector attaches to? Thanks!