Hello, I just got notice of your question. There have been problems with the inter webs today.
Please attach a well focused, close up photo of the wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.
You can use the paper clip- icon at the right end of thetool bar at the top of this dialog box to attach it here. ,Include a picture of the thermostat wire connections to the printed circuit board in the same area.
If there is no paper clip-icon, look for the '+attach files' link at left of your send button.
I can mark it up with trouble shooting instructions.
The lack of an error code however points to a bad printed circuit card... lets do a heat stress test on it.
Use a hair drier to slowly and gently warm the card to 120F(warm to the touch but not hot and not over140F)... if you get any change in behavior that means the card is bad.
A micro crack has opened in the printed circuit at a solder joint, or inside its CPU in that case .... or a short circuit has developed as the card expanded when you heated it.
Constant expansion and contraction as these electronics heat and during their duty cycles over the years is what wears these cards out.
It is also a good idea to replug all of the connections in the unit,that burnishes any oxidized terminal connections and will sometimes solve the problem, especially at the printed circuit card and in any sensor molex connectors. Do that with the power off to the unit of course.
We can go from there without a time limit.