Real_Beer, thanks for that really helpful post. When I ran the test with the serial monitor it was with the probe plugged into its socket. Tomorrow I will try switching the two wires around for the temp probe. Fingers crossed!
I have a suspicion that maybe something is going on with my circuit causing the LCD to go crazy, considering the 20x4 display shat itself, and the current 16x2 one seemed to be working normally for the first half our or so.
And failing that I will have a real good look through all the boards and see if i can find someone with the same problem.
I'm thinking I might just hook up a STC until I can get this sorted.. Or I could just keep using my inlaws grainfather... But it's way more fun making beer on a home made setup
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