I installed a Honeywell thermostat last year for our boiler and it worked perfectly. This year we were having issues with it not following the program schedule. The thermostat should be sleeping and then will turn on. I took the faceplate off and there is yellow goo inside on the components. Is this just a faulty thermostat or is something else going on? Honeywell has been no help when I have tried to contact them. Thanks!
That appears to be dielectric grease. It keeps the pins from corroding. I wouldn't have expected to see it on an interior thermostat, but it's not a concern. (It was probably there when you installed the thermostat.)
You can wipe some of it up, but try to leave a thin film on each pin.