The S1 Cafe - Helping Your Espresso Dreams Become Reality

Hiya,

On my machine (Mini VII) somethings "not right" - the espresso tends to taste bitter and never quite feel right. I've looked at all the obvious things and can't see anything so I've started looking at temperature. My machine is set to 94 degrees, with an offset of +3. I've got my trusty Fluke and a 'K' thermocouple. I've reference checked it against boiling water and it seems accuurate to 0.5 deg (C!)

Checking water exiting the group head after 20 mins warm up seems to be around 78-80 degrees which seems far too low. Filling a portafilter with ground coffee and wedging the thermocouple and pulling a (rubbish) shot seems to read the same. If I check water coming straight out of the steam boiler via the spout it seems to be around 95 degrees which is closer to what I'd have expected...!

Should I be expecting this and am I missing anything obvious? Is there a reference resistance I should be able to meter on the boiler sensor at room temperature? (or a chart!) - also are the steam and espresso boilers the same sensor? If so, I should at least be able to reference one against the other...

Does the front panel temperature display indicate that the group boiler is up to temperature? If yes, then the most likely failure is the temperature probe itself. As I recall, the V2 Mini uses a different style temperature probe on each boiler so you won't be able to easily swap them to see if that fixes the issue. Fortunately, the group boiler temp probe is fairly cheap.

Supposedly the machine will turn off if the boiler doesn't get to 60C within 5 minutes so that must be happening OK. This also seems to point to a temp probe issue. If your machine is less that 2 years old that part should be covered under warranty.

Thanks for that Chas. Yep, it thinks temp is up at the set point. The probe is about £40 in the UK which is about 8 times more than the basic component cost (typical vendor mark up!) so was hoping to nail down the likelihood of its failure a bit more tightly before ordering one - P&P is pretty high too!

I managed to find references to a PT1000 resistance table in other threads (via google - forum search seems to be down) but also contraditory comments saying that its actually a different sensor, is there a definitive resistance (range) that I should expect at room temperature to sanity check? Im curious as it seems when others sensors have failed its a major over / under heat that makes it obvious rather than being out by 15 degrees...?