This is a common issue with some brands of commercial coffee machines that fill the steam boiler directly from mains pressure. Often a valve will get stuck open and the steam boiler will overfill.
But this model fills via the pump from a tank. So whats the story?

On this little domestic Vibiemme coffee machine the customer reported that no water was flowing but as soon as I had it on the bench I noticed the pump running extensively with everything closed, then of course the steam pressure went very high and water came out the steam arm.

So why would the controller be telling the machine it’s got a low water level in the steam boiler when it is fact full to capacity?

1. The level probe is probably covered in scale.
To remove and check the level probe is a little difficult. the boiler can be unbolted at the base of the machine to allow it to slide back slightly. However the heat exchanger also needs to be unbolted and the steam arm. You have to do this or its not possible to get at the probe.
Always clean the probe.

2. The earth wire is poorly connected to the boiler body. Very common issue.

Just a note on temperature control on this machine. I noticed the pressure switch was set at 1.5 bar which is on the higher side. This is obviously an attempt to get hotter coffee water out. The best I could achieve was 81 degrees. This is not great and a problem with these little heat exchanger machines. Twin boilers allows for much better temperature control.

3. The main board is failing to recognise the water level.

The solution in this case was a failed control board, causing the pump to run continuously to fill the steam boiler. These control boards are basically just a water level detection circuit. And this can fail and the elements and lights etc still come on. You can run the boiler dry and cook an element, in some models.
Test the water level detection is working by pulling the wire off the probe and waiting to hear the pump kick in. Then put it back and the pump will stop.

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