Electrical gremlins,expert needed

Hi all.My 2014 2l diesel Octavia is suddenly showing various faults.Started with dpf error,cleared the fault with a OBD scanner.Next day the EML came on.Cleared that and it ran fine for a few hours.Next day the glow plug symbol was flashing and it basically went into limp mode.Then the EML came back on.Took it to a garage who have said they suspect a poor connection going to the ECU as it is only getting 4 volts when it should get 5 volts apparently.They are supposed to be investigating further but so far have not come up with anything.A few weeks ago the radio volume button stopped working.It has happened a couple of time since but is ok after turning ignition off.Also I have had the heater blowing out cold air when set to hot and blowing hot air when set to cold.No idea if any of these things have a common root cause or not.Anybody have any idea what is going on with the car and how I might rectify it? I am taking it to another garage tomorrow but as I have no knowledge of car electrics,I am hoping someone on here may have had a similar problem and may know of a solution.Thankyou for your time.