Ok--I didn't fill up the water tank properly and even though the tank wasn't empty it still set off the thermal safety switch on my 3-4 year old Nuova Simonelli Oscar espresso machine. I opened up the top of the machine and located on the right side front what I believe to be the correct switch--a red button which in fact is more of an inch long wand than it is a button. It won't push in but it does pull out a small bit. I close up the machine and try to start it. After pressing the start button on the machine, nothing happens. Usually my procedure is to push the start button, wait about 15 minutes while the water heats up, turn the steamer wand on for about 5 seconds to release pressure, turn the steamer wand off and go on to make espresso. Now, the only way I can get the machine to heat up is to turn the steamer wand fully on right away after I've pushed the start button and wait until the water starts to hiss, turn the steamer wand off and wait a minute or two for the steam to build up more, turn the steamer wand on again to release pressure, and then go on to make espresso. Since many people seem to follow this procedure anyway, I assume it's ok to do this. But why won't the thermal safety switch reset properly? Does it need replacement? Any suggestions?
By the way, I think this is a great machine!

steveb wrote:Now, the only way I can get the machine to heat up is to turn the steamer wand fully on right away after I've pushed the start button and wait until the water starts to hiss, turn the steamer wand off and wait a minute or two for the steam to build up more, turn the steamer wand on again to release pressure, and then go on to make espresso. Since many people seem to follow this procedure anyway, I assume it's ok to do this. But why won't the thermal safety switch reset properly? Does it need replacement? Any suggestions?
By the way, I think this is a great machine!

So, it gets hot but not hot enough until you've opened the steaming wand a couple of times?
If so, then the problem isn't the overtemp protection; looking at the manuals for this machine it appears that it doesn't have a vacuum breaker, so releasing the "false pressure" by opening the steamer wand is not unreasonable.

when is the last time you descaled?

Thanks for the reply. Actually, the unit doesn't heat up at all after I push the start button--until I open up the steam wand. After this it starts to heat up, and after 5 minutes or so I turn the steam wand off until it finishes building up steam. I then turn the steam wand on to release pressure. Then I start to make espresso.

I've never had it descaled. I bought it used less than 2 years ago, making one double shot nearly every day. I clean around the screen after each use and use only filtered water. I don't notice any funny smells anywhere. When I open up the machine and look inside, everything still looks new. I did a backflush on it when I first got it but nothing since. Would descaling the machine fix the problem of it not heating up the way it used to? How do I descale it?