Pretty much finished 'PiAndMash' - that's what I'm calling it.
Got the HLT being controlled by a PID class. That's a science in itself! PID tuning who knew. Using Pigpiod to control the GPIOs on the Raspberry Pi - saved me having to run my code as root. The developer was very helpful - My DS18b20 sensors kept dropping out using his daemon - wasn't his fault at all - turned out that Kivy was using more 40% cpu - which prevented other threads, and the sensor driver, getting enough time on the CPU. I dropped the Kivy framerate to 30fps, and it fixed it - don't need 60fps for brewing software!
Had a bit of a game trying to get the software to auto launch on boot. Easy if your software uses X11, but a non X11 GUI is another thing. In the end I modified /etc/inittab to log a normal user in without password by replacing this line:
1:2345:respawn:/sbin/getty 115200 tty1
...with this line:
1:2345:respawn:/bin/login -f sysop tty1 /dev/tty1 2>&1
...then launched Kivy from .bashrc works like a charm.