C_C esque fireworks... you cheeky monkey. The only fireworks were the loud swearwords I shouted as I shaked blood all over the kitchen floor. What a mess. Now you can see why my avatar is Mr Bump...
My PID settings after auto calibration are:
P = 02.4
I = 0099
d = 024
SF = 001
Bb = 038
ot = 002
FILt = 0
..but bear in mind my thermocouple is on top of the boiler as stated previously, not at the side where the thermostat is. I think the thermostat is positioned too close to the element anyway. I mean, the heat is going right to the thermocouple on yours through the boiler body, so you've much less chance of getting a decent measurement of the water temperature. I would suggest siting it at the front near the bottom of the boiler and re-doing the auto-calibrate.
Ally enclosures are fine. The best way to cut them prettily is to use a sheet cutting device called a nibbler, but you have to drill holes at the corners. It is earthed, right?
Following your comments about temperature, I've altered my set point to 92 degrees C. The HasBean Cup of Excellence is waiting for the machine to warm up even as I type. But the temperature is all over the place, so I think it might be necessary to recalibrate it. The coffee's not very good either.
Never mind, time for some more experimentation.
Edit : Just found out I had a loose connection to the SSR's low voltage supply (a couple of PP9s in series)... sorted now - let's have another go...