Autofill System Explained

The autofill system’s job is to ensure your boiler’s water level stays right where it’s supposed to. Too little water? You risk melting down or blowing your heating element by exposing it to air. Too much water? You risk no steam in the machine or worse a flooded cafe.

When a machine is first powered on, one of the first things the machine checks for is the correct level of water. Once the machine completes that check, it will heat to the correct temperature. Throughout the day the machine will need to refill to maintain the correct water level. As you use your machine water level decreases as water dispenses via the hot water tap and the steam wand.

Water level probe


The water level in the boiler is maintained by using a number of different components. The water level probe, also called liquid level probe or the auto-fill probe, is the most simple component of the system: a stainless steel rod which penetrates the boiler and contacts the surface of the water inside the boiler. Though very simple, it is often the cause of most autofill problems. A lack of continuity on the level probe will give a false reading and lead to fill issues. Removing the level probe, checking for continuity, and correcting the continuity issue (if there is one) will rectify many problems.

Pro tip: If your level probe is in your sight glass remove it! The lower sight glass tube is prone to clogging, and giving a false read and a false sense of security. If that’s where the level probe is reading from, remove it and install your anti syphon valve there.

Autofill solenoid


The next component in the autofill system is the autofill solenoid. When the level probe reads water is needed, the refill or main board triggers the autofill solenoid to open. This allows water to pass, fill the boiler to the correct level, then it closes to stop the water supply. The solenoid can fail either open or shut.


What do I do if my espresso machine is overfull of water?

If the autofill valves fails open, you’ll experience a machine that becomes overfull. First check of your level probe inside the boiler is working properly. If it is, check the solenoid valve.

What do I do if my espresso machine is underfull of water?

The solenoid should be the first thing to check, it is also the easiest. If the water pump is running and the machine is trying to fill, but not making any progress, the solenoid may be stuck shut, not allowing water to fill the boiler. You many want to remove the fill tube from the solenoid to the boiler and see if there is any water flow.