There’s lots of information on thermostats. A short, but mercifully brief internet search will reveal all types of definitions and descriptions of various types and designs of thermostats. From my limited reading on the subject, bi-metallic snap is the most likely type we have in our single boiler, vibe pump, non-E61 machines.

Suffice, to say, these simple devices use dissimilar metals that expand or contract and actuate a contact which turns on [or off] a heating element.

Therin lies the problem.

These mechanical devices may not be accurate or there may wide variations in performance. I am inclined to think they are as individual as snowflakes. Worse, they may “drift” with time – sometimes getting hotter or sometimes getting colder.

If a thermostat is going bad, you may luck out and find that yours is getting hotter. For instance my Gaggia Classic brewing therm runs “hot” at 205F or more. I have to actually do a cooling flush in order to get it down to the 200F range. [I take great delight in pretending I have a E-61 group]

Luck is smiling once again as my steam therm has suddenly decided I can now steam 12 ounces of milk to 160F without breaking a sweat. Before this, taking 10 ounces of milk to 140F was a challenge before the dreaded “temperature ready” light came on.

Moral of the story?

Proof your machine by checking your temperatures when you unpack your new machine.

It would not hurt to check your machine occasionally just to keep tabs on those mischievous thermostats.