Two of the most common problems in the steam department of home espresso machines are:
1. Lack of cleaning
2. Air locks
This blog is based on the assumption that the machine is actually producing steam
Today most modern espresso machine steam wands come pre-fitted with an "auto-frothing" device, whilst being a very clever idea, guaranteeing foam when working properly, they can also be very frustrating to use. The main problem is one of cleanliness.
If the holes which let in the air within the frothing device become blocked you will end up with some very hot milk but no foam. For foam to be created air has to be driven into the milk by the steam. What I have found on many occasions is that the user is unaware that the frothing device can be taken apart and washed, as a result the foam mysteriously disappears and the machine gets blamed for its inability to create vast quantities of foam.
Foaming devices can be easily pulled apart - once inside you will find lumps of dried milk - give each part a good clean, reassemble and hopefully frothy cappuccinos can once again be yours.
If this doesn't cure the problem then issue two as mentioned above, an airlock is likely to be the cause of your problems.
Airlocks can be created if the machine runs out of water and can usually only be removed by driving water through the steam wand and group head of the machine. This is done by opening fully the knob that controls the steam and then switching on the pump that is usually used to drive water through the coffee.
Place a receptacle under the steam wand to catch any water that comes out - When you have a good flow of water, turn off the pump, and shut down the steam wand using the controlling knob. Allow the machine to heat up again and hopefully steam pressure will have returned.
As I experienced the other day, this proceedure may need to be carried out two or three times to remove all airlocks, do persevere because unless there is a more major problem such as an element failure in the machine (which would mean that no steam was being generated) it should be perfectly possible to achieve a good steam pressure once again.
Enjoy your cappuccino!