Honeywell Electronic Programmable Heat/Cool Thermostat - CT3300A100 Heater "expansion valve stuck open" Questions

...Expansion valve, witch will require opening the system. I suggest a service professional as Freon is hazardous, and being wrong is expensive. It could just be that the rheostat on he control knob is ...

...valve and is not letting it seal properly. It could be that the expansion vessel that takes up the extra pressure when the water heats and expands, has lost its pressure and needs represureising. The ...