It’s a waste of tome running water through the brew head and measuring it’s temperature. It needs a scace Complicated by pre infusion even then. There is a video of a DB using a scace on youtube, I might knock one up one day :) but @DavecUK probably wont tell me what he uses as a grinds substitute.
I’ve left my new DB OPV at 10bar. LOL So am using it as Sage intend. Brew pressure varies a bit according to beans. 9 to 9.5bar. That should allow the volumetrics to work but still working on shot consistency. Now very genera;;y fixed 30sec giving ~2g range on a 30g shot from 12.7g. The ratio on my monsooned is now lower than it was. Don’t think that is down to 9.5bar. More likely to be more even extraction throughout the puck.
Using the DB. Turn it on. Weigh the beans, grind - in the Niche cup again, Bit of stir. Into the portafiter. Level, tap down ;) usually level a bit more. 2 slope leveller, tamp. The machine is usually showing 93C by then so pull the shot. Shot or shots done - turn it off.
Some fit the portafilter and allow that to heat up first. I’ve found no need using a bottomless portafilter, No taste change, Heating that would probably add ~10min.