Have HVAC Questions? Ask an HVAC Expert for Answers
Hello, the situation with the wire is that both shielded, and unshielded cable can be used. Unshielded does not resist electrical interference from outside sources as well as shielded. You most likely have unshielded cable.
You can inspect the cable and if there is no foil wrap around the wires inside the cable jacket, then it is unshielded.
I have seen extreme cases where unshielded cable, such as you have, works well .... but sometimes there are electromagnetic influences on the communication cable that will produce the communication error you are reporting.
Since however your system has been working well since 2008 it is not likely replacing your communication cable with shielded cable will solve the problem. But it might (10% chance)
There is most likely a problem with the thermostat or the printed circuit board inside your air handler that is at fault. Its a tricky diagnosis.
Tell me a lot about your skill sets so that I can coach you most effectively.
We can go from there.