Although the exterior group temp is indicative, it allows me to pull consistent shots over the years. Others find the same. The boiler pressure is not a good indication. I learned long ago to have the boiler pressure cruising at a level below maintaining sufficient brew temperature at the brew group and using half pumps to bring the group up to the desired temperature. That temperature will vary, depending on where you have the probe located. But once you know the numbers for your machine it'll work.

For a 2nd generation La Pavoni like yours, if you leave it on, group temperature will tend to get too hot on successive shots unless you toggle it off. You read that of course in the Om Zone section.

I think of these La Pavoni levers as having the ability to temperature surf, given appropriate technique. Others see them as unstable and go to all kinds of lengths to modify the machine to overcome that. One of the best I've seen is to convert the steam-heated group into a water-heated one, as it is in the first and third-gen machines. However, the Zen Zone and Om Zone techniques are sufficient.

Let me suggest this. Place a temperature probe on the outside of the group and leave the machine on the low setting and venting (taking care not to boil it dry -- I write this for others, you've shown some great skills in your restoration). How high does the temperature climb? Is the brew temperature too high?

You could also do temperature studies inside the group, which would require putting a thermocouple into a sacrificial filter basket and comparing that to external temperature. Maybe someone has already done this.

The Cremina temperature study done long ago will give different results, because it has a water-heated group.

Olympia Cremina Temperature Study, Part 1