Your plan doesn't sound like a prediction model. It is more like an alert when present situation is different than normal/average behaviour.
Simple solution:
You can calculate simple mean of your temperature AVG measurements and its standard deviations SD.
Then you can rise an alarm if present temperature does not belong into interval (AVG - alpha1*SD, AVG + alpha2*SD), where alpha1 and alpha2 are some constants.
Those constants depends how much dispersion from the mean you are able accept as normal. alpha1 and alpha2 could be equal, but it is up to you if you want symmetrical interval or not. For example, you can accept AVG - 3*SD temperature, but you will want to rise an alarm if temperature exceeds value AVG+2*SD.
Add some complexity:
Will you be measuring the temperature 24h per day or just when 3d printer is on?
If you think about measuring the temperature 24h per day you'll have to face cyclical behaviour - you will have different values temperature at night and during the day and also it does matter if the 3d printer is on or off.
So, the simple model should be divided (your measurments) on some time intervals conditionally if your 3d printer is on or off.