Maybe it's the grind. You're going really fine and the puck prep is channeling. If the extraction tasted bitter, that might be it. Try coarser with better puck prep.

Puck prep is an important variable. Dose, distribution and tamp make a difference. From there it's grinder and machine variable controls. Grind is reflective of burrs and alignment. Machine variables are pump pressure, preinfusion, basket quality, showerscreen quality/water distribution, extraction control.

And then there's roast quality. It's hard to extract a stale roast ideally.

Try to isolate them. Maybe use a good roast, find a good fine grind setting, stay with the basket dose weight, RDT and WDT the grind and try to choke the machine. From there go coarser with all other variables remaining the same until you find the even flow rate that tastes good.

I will upload something once I get home today of just the bare grouphead. No, I brew first than steam. I have already taken out the solenoid valve and cleaned it. I'm thinking to replace the thermostat regardless. I may also need to shim my grinder.

Based on my earlier video it doesn't seems like it is channeling, but I can be wrong. I've also played around with the grind from finest to medium coarse, with little change in extraction time.

Yes, the temp surfing idea is something like that. Mostly it is an attempt to have a consistent temperature from shot to shot. But if the boiler is too hot, it should also cool it off and you can pull the shot before it re-over-heats.

The routine is something like run for 5 seconds, lock in, pull. You need to experiment.

The PID with a thermocouple instead of the thermostat will show you the real time temp as well as the target temp. It is also helpful for steaming if you are making milk drinks.

Where is the video with the flush to check whether the boiler temperature is higher than the boiling temperature of water?