you also delete...

Yes definitely, I did not add that part but it should be deleted, will add a possible snippet to the code above, thanks

To follow up on what @SGaist said, what I normally do is not to create the serial port in the constructor of the Comunications class (assuming you do), but connect a slot in Communications to the QThread::started() signal, and in there create the serial port. That would ensure that when the serial port class is created that it will be created in the thread that needs to use it.

class Comunications : public QObject {
public slots:
    void threadStarted() { 
        d_serialPort = new QSerialPort();
        // ... <- set up
        d_serialPort.open();
    }
    void threadStopped() { 
        d_serialPort.close(); // Might not work/be needed
        delete d_serialPort;
        d_serialPort = nullptr;
    }
private:
    QSerialPort* d_serialPort;
}; 

and then in your constructor

com = new Comunications();
thread = new QThread(this);
connect(thread, &QThread::started, com, &Comunications::threadStarted);
thread->start();

As @SGaist pointed out, make sure to clean up objects created:

connect(thread, &QThread::finished, com, &Comunications::threadStopped);

PS: Please put your code into code blocks when creating posts
[edit: added example code for cleanup]

@yoavmil Are you trying to suggest to call moveToThread on an unallocated object ?

@Sergio I guess your Communications class contains a QSerialPort ? If so, did you give a parent to your QSerialPort instance (i.e. _serialPort = new QSerialPort(this))? From the error message, probably not, hence it's not moved along with your Communications instance.