Low water pressure does not make foam of espresso.

If you're experiencing issues with the steam function on your Rancilio Silvia espresso machine, such as low steam pressure or no steam at all, there are a few possible causes and troubleshooting steps you can take to address the problem:

1. Check Water Level: Make sure the water reservoir is filled with water to an appropriate level. The steam function requires sufficient water to generate steam.
2. Purge Air from Boiler: If you're getting low air with no pressure from the steam wand, it's possible that there's air trapped in the boiler. You can try "purging" the air by turning on the steam wand and letting water flow through it until a steady stream of water comes out. This might help remove air pockets from the system.
3. Steam Wand Blockage: The steam wand could be partially blocked by milk residue or mineral deposits. Clean the steam wand thoroughly using a steam wand brush and ensure that the tip is clear.
4. Vent Valve: The vent valve on the top of the steam wand might be clogged. Try removing the valve and cleaning it to ensure proper steam flow.
5. Boiler Pressure: Low steam pressure could be a result of inadequate boiler pressure. Check the pressure gauge on the machine to ensure that the boiler pressure is within the recommended range. If the pressure is too low, you might need to adjust the pressure settings (if your machine allows for it) or seek professional assistance.
6. Steam Valve: The steam valve might be worn or malfunctioning, preventing proper steam flow. If the steam valve is not functioning as it should, it might need to be repaired or replaced.
7. Boiler Heating Element: If the heating element in the boiler is not functioning correctly, it could lead to low steam pressure. Check for any signs of damage or malfunction in the heating element.
8. Professional Service: If none of the above steps resolve the issue, it might be best to seek the assistance of a professional espresso machine technician. They can diagnose the problem accurately and perform any necessary repairs.

Remember that working on espresso machines involves potentially hazardous components and high-pressure systems. If you're not comfortable with any of the steps or if the issue seems complex, seeking professional assistance is recommended to ensure your safety and prevent further damage to the machine.

Similar to the crema on quality espresso, this "foam" is an indicator of the freshness of your coffee. If it's thick and creamy white, it's very fresh. If it's present but thin and watery, it's less fresh.
https://www.quora.com/What-is-the-foam-on-coffee-made-of-that-appears-on-milk-based-and-even-black-coffees
The foam found at the top of your cup is "crema" comes from the espresso making process. Espresso is prepared in a metal contraption, which you pound down and hot water is pumped through at great pressures. The pressure pushes out the little oils from the coffee beans into the liquid. https://www.joyridecoffeedistributors.com/blog/coffee-news/where-does-the-foam-come-from

If water/pump pressure is below 9 bar, then you will have to adjust the pump. Remove the right side panel, pump is usually located there, find the big brass head with 2 water lines coming to it, on the side of it is an adjustment nut and or screw depending on pump model. Adjust tighter gives more pressure.

It's clogged with scale, use citric acid to descale and use only bottled water

Descale machine before thinking of replacing, it might be cheaper to rebuild unit than replace.

There is a low water sensor tube in the water tank. Pull it out and leave it out for 30 seconds, then lower the bell back into the water tank. If the bell gets water inside the it looses the aire pressure to activate the sensor. There should be only air in the bell and hose.

The head could be blocked up.
Remove the head via the 2 hex screws,inspect and clean as necessary.

Check screen and diffuser for blockage, backwash machine. If you still have the noise problem, when runnig the head, then it is block at the solenoid. For the temperature, it is possible that the one of the thermostat is damaged.

Perform a full descale cycle to clear the steam boiler of any debris or build up. Most likely due to blockage.

you both can have same problem, solution is:

1. low pressure of pump (or too fone grinded coffee)
2. security valve of boiler openes to early and dont let the pump to rise pressure enough for good brewing( if it is this you can see water returning back to container if you have 2nd pipe in your machines reservoir)