Lift the lever, but nothing happen - no sound, no...

Question

Giotto has worked fine for a couple of years until recently. I lifted the lever, no coffee comes out. I try any possible ways including draining all the water from the tank and restarting the machine. It just won't brew again. The pump should be working since I heard it's usual loud noise sucking the water from water reservoir to the boiler. The boiler is working fine, too. The steam pressure built up till 1~1.5 as usual. I suspect either the switch or the sensor is broken. Any idea to help me debug. Thanks!