I see the Gaggia Classic Pro has some issue with the temperature as it uses a hysteresis to do bang-bang control. This is not necessarily something bad but from what people say the bands are quite big.
The common solution to the problem is to buy a PID kit with display, possibility to change the temperature setpoint and a shitload of crap.
However, to fix the problem you could just change the hysteresis limits so the bang-bang controller is faster to react and there’s less temperature difference. I have not looked into how to change these but I would imagine it would be a matter of some small soldering and a few cents of components vs 100 usd. Perhaps you can get away without soldering? Has anyone looked at this option? Of course you will use more the relay and may need to change sooner but these are also dirty cheap.
While the PID is primarily installed to fix the temperature stability issue, it also allows you to adjust your brew temp if you want to try a 90-degree shot and then crank it back up to 98 for a different roast.
People talk a lot about how the Gaggia doesn’t hold temp while brewing, but the boiler can also get too hot, hurting your shot.
Exactly. Mechanical thermostats can also be unreliable over time as they continue to heat cycle which will eventually incur plastic deformation and lead to leading and lagging temperature engagements. Prefer not to have to swap out a thermostat every time I want to change my temperature let alone after they start to drift or fail. Installing the PID is not that cumbersome even for those that are not that handy.