Hot water only with the the setam switch on

From your description and info replace valve.

Use Citric Acid.

1. Dissolve about one tablespoon of citric acid in the water reservoir.
2. Fill the boiler completely. Open the steam valve and start a hot water cycle until water comes out the steam vent. Stop the hot water cycle, close the vent.
3. Let the boiler heat up about 5 minutes. Then turn off the power.
4. Let the acid solution work for about 1/2 hour.
5. Pull a 30 second shot to change the water in the boiler.
6. Repeat flushing cycles (steps 3, 4, & 5) until the water looks clear. Refill the reservoir with water and acid as needed.
7. Wash out the water reservoir.
8. Pull 5 or shots to get the acidic water out of the boiler. Run a hot water cycle to clean the acidic water out of the steam vent.
9. Let the unit come to temperature and look for leaks.
10. Make some coffee and look for leaks.
11. Froth some milk and look for leaks.

Remove the top panel, and check the thermostats on the boiler there are 3 of them. One needs to be reset.

Machine is not heating, the lights should flash until it heats up to 1.2 bar on the top gauge. If not check the water level in the machine and check the red reset switch to see if the thermostat tripped.

Unplug machine and remove the top panel, check the thermostats on of them tripped reset and you should be back in business.

I would check the temperature of water. Sounds like it might be too hot. The temp of the water should be between 192 and 197. Colder and its sour, and hotter and its bitter.

Remove the top panel and check the 3 thermostat on the machine one of them is not functioning properly, find the wire to the steam switch and trace it to the thermostat.

parts and pictures here

Rancilio Silvia Parts

Hi
Do an ohms check on the element. With an ohms meter check the reading between the elements. The reading should be between 12 and 16 ohms for a 110v machine and 50 to 60 for a 220v machine. If you have no reading or a higher reading you have a bad element.
Replace the boiler

Yes there is a small red breaker switch on the left side of the boiler tank. Unplug the unit first then remove the left side cover and just push down on the red breaker switch to reset it.