Strange HVAC problem

[Zinger]

Apologies if this isn't 100% on topic, but if you guys can't help me I'm going to have to find an exorcist.

I'm having a truly bizarre problem with my home HVAC system.  It keeps turning itself on, switching between heating and cooling, and resetting its temperature.  Even if the thermostat is set to off, it will come on by itself.  It usually happens in the middle of the night, but it occasionally occurs during the day.

Last winter, when it was 20° out, it switched itself to air conditioning and set the temperature to 60°.

The HVAC unit is a 6 year old Bryant 313AAV/JAV.  The original thermostat was a Honeywell TH6000 series programmable.  I switch it out for a TH3000 series non-programmable, thinking the thermostat might have been the problem. That made no difference.

Honeywell's help line thought it might be a short in the wiring between the thermostat and the HVAC.  I had a technician from John C. Flood check it. He found no problems anywhere in the system and couldn't recreate the problem, of course.  BTW, Flood installed the system 6 years ago.

He suggested switching out the control board in the Bryant, but didn't sound hopeful.

Any ideas on what could be causing this or advice on how to trouble shoot it?  I'm literally losing sleep over this.  I keep waking up to see if it's done anything funky.

Thanks.

[Samogon]

Control board is most probable cause. Chech is moisture gets into it, corrosion, etc.
So technician most likely right

[Armadillo]

Is this thing under remote control? Hide your remote control far away. I had a friend, his remote control gone crazy. A closer inspection reviewed that moisture had gotten into the remote control.

[james_s]

Look for bad capacitors on the control board, particularly in the power supply. Wonky power supply can cause all sorts of weird stuff.

[Cyberdragon]

How could capacitors go bad in only 6 years? Are they being abused (IE getting hot, excessive vibration, exc)?

It could also be an open control bus (either a wire or part of the circuit board) or a bad bias resistor on a data line to the thermostat allowing stray signals to get into the digital control system.

[james_s]

I've seen loads of bad capacitors that were not even 6 years old, it's very common. Especially if it has a switchmode regulator and cheap capacitors. I think I went through 4 or 5 AC adapters on my internet router before I finally switched to the old iron transformer type. I would expect a HVAC system to be better built than that but I wouldn't count on it.