I have a Gaggia Classic. It makes perfect espresso/cappucino - up till now. Suddely the the pressure on the steam reduceses after a short while, and I can't froth the milk. What is wrong? I have descaled the machine.
The first thing I would check is the steam thermostat. On top of the boiler is the thermostat. Remove the wire terminals. Unscrew the thermostat. Check to see if there is a good supply of heat conducting paste on the bottom. If not, that is probably your problem. Apply some more and reinstall.