My Rancilio Silvia brews fine but does not produce enough steam to froth even one cup milk after oulling a shot. Starts off with steam from wand but then what appears to be hot air only comes out of wand and doesn't froth milk. If I re-prime the reservoir things seem to improve and I can froth the next cup. The problem seems more noticeable if I let the machine warm up for 10-20 minutes before brewing. I run about 2 cups of water through the brew group before pulling the first shot every day. The machine hasn't been used that much and has never overheated as far as I know. Also (if this helps) the brewhead will spit out steam and water rather than just water between successive shots of espresso (no frothing in between) if I let the machine warm up for 10 minutes or so and fully prime the group. Thoughts?

Silvia has two bimetalic switches that control the boiler temperature. One for brew water and one for steam. They are not exact and they can go bad. They are cheap and easy to replace. Just Google for Rancilio parts.

A much better fix (and more expensive) is to switch to PID control. Google for Rancilio PID control. The conversion is $250+ but once you've gone PID, you'll never go back. The temperature is exact, fast, and totally under your control.

The steam wand ejects steam in order to froth the milk. The steam wand should be cleaned after it is inserted into milk and at the end of each day. Do not allow the steam wands to soak in water overnight since some of the dirty water can be sucked into the boiling tank inside the machine this may cause the steam not to come out
Unplug the machine, take the case off, disconnect the switch wires and test it with a continuity meter. If you don't get any continuity, or if it is constantly closed and never open, the switch is bad.
this could have been prevented by regular maintenance and proper use. The usual suspect is a gummed up wand or brew line or user error. Here’s what to look for and how to avoid it.
First, notice what kind of wand you have. Most semi-automatic and porta-filter espresso units will have wands that resemble those on bottom or right, although the tips may be different. Some tips do not slide up and down to alter the aeration, as the one on the bottom does. If your wand is from an older (1990s) unit, it could have a more bulbous tip and a smaller hole in the tip. Some of the new wands give you a manual/automatic control.
Many of the new super automatics come with an automatic frothing unit, like this one from Jura-Capresso. The nice thing about the frothing wands on Jura-Capresso's new units is that they allow for even more control.
The "Dual Frother Plus" (top) works like the traditional frothing wand. The metal sleeve goes up for steam, down for foam.
The "Froth Xpress Plus" is a very handy device which can be used with the included sleek milk container or a distinct milk container, like a 1/2 gallon jug. The Froth Xpress has a tube (hard for using the included container, flexible for using a different container) that fits into the frothing tube behind the dial shown in the picture above. After selecting froth or steam, the milk is siphoned into a cup below the steam wand. We recommend steaming the milk first, then adding the espresso.

Whatever sort of wand you have, it is essential to keep it clear of solidified milk which can gum up the tip and even the wand shaft. Here are some symptoms of a clogged wand:

• Little or no steam comes out of the wand
  
• Hot water drips from the tip of the wand
  
• A squeal or whistle comes out of the wand when the steam function is selected
  
• A deep humming is heard when the steam function is selected*
  

*This is also a symptom of another more serious problem, particularly if you have a pump espresso machine; so if unclogging the wand does not solve it, you should contact a technician.
A good preventative measure against the clogging of a steam wand is regular rinsing in warm, soapy water of the tip and any other removable frothing part. This should be done after each steam wand use. If your machine has a Froth Xpress, it is important to clean all of the hoses, valve, and connectors (be very careful with the plug, however, because it is delicate). All wands should also have steam jetted through them after a frothing cycle is run.
Another preventative measure is to run a steam cycle for about twenty seconds before each new use. This will eject stray particles before they can build up and cause serious damage. There is also a cappuccino cleaner available which can be used in the automatic frothing devices. The solution is placed in a reservoir, and a full cycle is run until the reservoir is emptied. This can be done every few weeks or every few months, depending upon use.
Aside from prevention, there are treatments for a clogged wand. First, remove the tip, if the tip is removable. Usually they are, as in the case of the plastic tips above. The holes are usually big enough to run a pin or even a small paperclip through (emphasize small) to remove the gunk. If these items are too large, do not attempt to use them; instead try using a thin gauge wire from an electrical wire strand. Next, the metal wand itself can have a pipe cleaner run up into it. Start out by putting just about a half inch of the pipe cleaner up the wand, rubbing it around, then pulling it out. Gradually work more of the pipe cleaner up the wand, but never let the length of pipe cleaner in the wand exceed the wand length. We recommend the pipe cleaners with the stiff barbs attached, as opposed to the mostly soft ones. Do the same for all of the hard hoses and connectors. With respect to rubber or soft plastic parts, rinse them in soapy hot water. If flexible hoses form holes, replacements are available (give us a call) or we've even had some luck at aquarium supply stores.
PLEASE NOTE: if you own the Jura X7 or the Froth Xpress Plus, the diameter of the tiny holes is very important. We recommend trying not to put pins into these holes. However, if they must be cleaned and soaking won't work, a smaller gauge wire, a single strand, should do the trick. Always use a strand that is smaller than the diameter of the hole.
Frothing wand technology is advancing at a breakneck speed, but along with these advances come serious precautionary measures for dealing with these very delicate mechanisms. Follow the steps above, and your machine should be producing full-fledged froth for its entire life.

Agree with previous suggestion. The steam pipe is most likely blocked and generally the blockage occurs in the bend of the steam pipe. Either try removing the wand and clearing it or use a thin piece of wire/pipe cleaner and insert it up the pipe. It could alternatively be a piece of limescale blocking it so it may be worthwhile to try descaling the machine if after clearing blockage. Hope this helps.

The steam wand to froth milk, you need a certain amount of milk in the cup first, then if you tilt the cup a little towards you, push the steam button and "it should froth your milk right up", but if that doesn't work then I don't know.

descale the heating elements with vinnegar.

This problem developed on my Sirena machine about a week ago. Stopped frothing milk, but still produced lots of steam. In fact, it was splattering milk everywhere, just not producing foam. Cleaned the steam wand (including air intake) and descaled the machine (even though its only 3 months old) to no avail. Called Saeco customer support (1-800-933-7876) and the very helpful rep immediately identified the problem. Inside the Panarello steam wand is a removable plastic tube. The tip of this tube should protrude about 1/8" beyond the end of the steam wand. Mine was not. Using the eraser end of a pencil, I pushed the inner tube downward into position and, voila, I now have froth again.

maybe is just air in pump,try prime water on steam wand.open steam valve and press button for make espresso,keep couple seconds

please relay on your experience realizing that you now have new steam pipe(with different holes in the end of it and different pressure)
you will need to get use to them and get maximum quality of that steam pipe.
my advice:

1. every time hold your hand in the bottom of milk container, so that you will prevent overheating which often gives the result you mentioned.
2. every time you use cold milk.
   

For the coffee - make sure the machine has heated up for at least 10 minutes. I've found the grind is the most important in getting a good shot of espresso with a good crema.

It takes trying different grinds to find what works best. When we grind at the store we choose the second finest grind from the finest - we put it to Turkish and then turn it back one notch.

On the steaming side - it takes practice. Sometimes I get froth, sometimes - I usually let the wand go near the bottom of the steaming cup and heat the milk to 160 deg. f.

If the milk scalds, you're getting it hot enough. It sounds like you're not incorporating enough air into the milk when frothing.
Make sure that the holes in the tip of the steam wand are clear. Soak in water for 5-10 min. and wipe with a cloth (no abrasives) and clear the holes with a paper clip end. Blow the wand out nice and hard.
How is your steam pressure? It should be about 1.2 bar.
It could also be your technique. The wand should never be more than 3 cm into the milk. For cappuccino froth, keep the tip right at the surface of the milk, lowering the pitcher as the level rises. You should hear a "shushing" sound, no squealing.

Good luck!