have now returned to the Developed World.
Arhhh yes....paranoid ! ;
Some background. If you are going to check the brew temp of an espresso machine you need to have a properly calibrated and fast reading instrument, and do it in the correct manner. For most people, that usually means, please dont use the milk thermometer! It does mean, using a specially set up group handle with facility for the calibrated thermocouple positioned inside the "group cup" of the group handle (ie the space where the coffee filter would otherwise live). There would also be an open/shut valve where the coffee outlets usually live, so that flow of hot water can be regulated (or not) through the group handle while the reading is taken.
One form of that is a thing called a "scace" device because it was marketed by someone called Mr. Scace, but he doesnt have a monopoly on that kind of gear and we were making them in house for our own workshop use likely before Mr Scace was even born.....
OR....there are some thermometers that can be fitted into the group itself and are on permanent display, but we dont use them and dont know how accurate they may be (however my peronal opinion would be that fitting one of those may actually cause paranoia as it allows you to watch *normal* temperarture fluctuations as they come and go, and obscess about whether there is something qrong with a machine or not....I prefer not to sell that stuff to people as it can just cause everyone to look for problems where there usually aren't any...).
Others have already advised, to leave your machine on for a minimum time before making coffee. 6 minutes is not long enough, and you probably found that the coffee had a yellow crema. That is a tell tale of under extraction from the brew water being under temp.
Further....at 6 minutes the water in the boiler has reached operating temperature and the pressurestat has switched off the element......BUT.....the group itself is still only luke warm. So if you make coffee then, the HOT water coming from the heat exchanger is actually COOLED by the under temp mass of the group (around 3 kg). Ergo: underextracted coffee from undertemp water. Despite that the element has switched off, the machine in toto is not ready to brew, until THE GROUP has also reached operating temperature. That wouldnt occur until around say 20 minutes in reality, although you can "cheat" the machine into being ready sooner by intermittently flowing water through the group at regular intervals from the point at which the pressurestat first switched off the element, until you can feel that the group has become too hot to touch. That is quicker than if you just leave the machine to heat passively at its own rate.... and is good for when you are in a hurry (I do it !).
If you use a well calibrated thermometer and you want a *rough* indication of the temperature of the brew water, note that if you simply stick the end of the (pre warmed, because these thermometers are slow to read and the coffee will be cooling while the needle is rising) thermometer in a (pre warmed) espresso cup while brewing coffee, you can expect to read a coffee temperature in the cup of roughly 70 degrees. That is quite normal. But as I mentioned earlier, its not a great idea to use a milk thermometer because they are not usually very well calibrated and they are slow, and who knows what the reading will show.
Ultimately, may I conclude so:
a) Machine not on for long enough before coffee was brewed or temp check was done,
b) accuracy and type of instrument used suss?
c) method of test suss?
Nothing to be concerned about, this is a very common concern amongst new machine buyers
Hope that helps,