Thank you for your help pylon!
It prints almost instantly now. It also prints out whatever it reads from serial.
There's problem tho:
Thermal.write(buffer, pos);
Gives the famous:
invalid conversion from 'char*' to 'const uint8_t*'
I've tried to cast but didn't work.
I've removed the pos arg from the write function. It compiled without any problems and as i've mentioned printer reacted instantly. But now most of the letters are broken (replaced by other ASCII chars]
I've used print instead of write as well but again no luck.
Thanks again for your help.