Seems very quiet here. Coffee must be out of fashion?

I have an espresso/cappuccino machine. It makes a
decent espresso, but its cappuccino has never been
much good. Lately it's got worse, the nozzle blows
steam vigorously; the milk heats up but remains
basically flat.

It would be great to learn the basic principles of
how pressurised steam froths up milk. With some
theory, I can at least make a guess as to how my
machine diverges from it.

Or is this a common problem with a standard solution?

Any suggestions?

--
Nick Kew